Therapeutic potential of allicin against viral infections: Mechanisms and safety profile (Review)

1. Introduction

Garlic (Allium sativum) is widely acknowledged for its notable antiviral properties, primarily derived from organosulfur components such as allicin (1-3). These bioactive agents such as diallyl disulfide (DADS), diallyl trisulfide (DATS) and ajoene have been found to suppress viral replication and strengthen the immune response of the host (1). Therefore, garlic may be a useful adjunct in managing respiratory viral infections, particularly in mitigating virus-induced oxidative stress (1,2,4,5). Current antiviral drugs, including nucleoside analogs (such as acyclovir for herpes viruses and oseltamivir for influenza) and protease inhibitors (such as ritonavir for HIV), exhibit certain disadvantages, including limited effectiveness against emerging viral strains and the development of drug-resistant viruses (6-8). This positions natural options such as garlic as a promising direction for further research and highlights that the development of novel antiviral drugs is key, especially during pandemics, as the coronavirus disease 19 (COVID-19) crisis has shown. Studies have demonstrated that garlic-derived compounds can inhibit severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replication in vitro (9,10), block viral entry into host cells by interfering with the spike protein-angiotensin-converting enzyme 2 receptor interaction (11), and reduce virus-induced inflammation by suppressing pro-inflammatory cytokines such as IL-6 and IL-8(12). Furthermore, a randomized controlled trial suggested that garlic extract as adjunctive therapy may reduce the need for supplemental oxygen in hospitalized patients with COVID-19(13). These findings underscore the relevance of exploring garlic-based interventions in the context of emerging viral pandemics.

Over the past century, natural products have been a primary source for drug development, with 60-80% of antibiotics and anticancer drugs being derived from natural products or their derivatives (14). Garlic is known for its diverse pharmacological effects, such as antibacterial, anti-inflammatory and antiviral activities (15). The antiviral capacity of this plant is mainly associated with organosulfur constituents, including DATS, ajoene and allicin (16). The latter, a sulfur-rich bioactive molecule, is produced upon crushing garlic through the enzymatic action of alliinase (17). Allicin exhibits a range of biological activities, including antimicrobial effects, immunomodulatory actions (such as enhancing natural killer cell activity, activating macrophages and regulating cytokine production) and direct antiviral effects (18-20). These antiviral functions are mediated through its ability to obstruct viral entry into host cells, suppress viral replication and modulate host immune responses to fight infection (21).

The pharmacokinetic profile of allicin demonstrates its efficient absorption and rapid metabolism, underpinning its potential as an antiviral agent (22,23). However, its use in medicine is limited as it breaks down easily and exhibits a strong smell, which has prompted a search for improved delivery methods (24). In response, research has shifted toward allicin-loaded nano-carriers designed to boost its bioavailability and shelf-life (23). Encapsulation of allicin in nanoparticles improves targeted delivery to infection sites, markedly strengthening its antiviral efficacy and reducing non-specific toxicity (23,25). These innovative systems improve the solubility and cellular permeability of allicin, enabling controlled release and expanding its potential applications in antiviral therapy, including enhanced targeting to infection sites and prolonged therapeutic activity (23,26).

Preclinical and virological investigations have revealed the broad-spectrum antiviral potential of allicin and other garlic-derived components, including ajoene, DATS, DADS, saponins and garlic extracts, as summarized in Tables I and II (1,21,27-37). In addition, to represent a translational perspective, Table III summarizes key human clinical studies involving garlic-based interventions for infection-related conditions (20,34,37-43). Against enveloped viruses such as influenza, allicin has been shown to disrupt viral integrity by binding to and oxidizing thiol groups in viral envelope proteins, thereby inhibiting viral entry into host cells (1). In studies conducted on the common rhinovirus pathogen, allicin and garlic extract have been shown to reduce viral RNA load, suppress virus-induced pro-inflammatory cytokine release (IL-6 and IL-8) and prevent epithelial barrier dysfunction in human bronchial epithelial cells (3,21). Furthermore, research regarding the hepatitis C virus model has highlighted the ability of allicin and its derivatives to modulate the cellular redox state and influence signaling pathways involved in antiviral defense (18,44). Allicin also exhibits marked antiviral activity against influenza A virus by effectively inhibiting viral replication by targeting and disrupting viral neuraminidase protein function, which is key in the release of new viral particles from infected cells (45). Finally, allicin has been shown to exhibit direct virucidal effects, meaning it can inactivate virus particles upon contact. This occurs primarily through binding to and oxidizing thiol groups in viral surface proteins (such as the hemagglutinin of influenza virus and envelope glycoproteins of herpes viruses), leading to protein denaturation and loss of viral infectivity (21,46).

Table I In vitro studies on the potential antiviral effects and mechanisms of garlic-derived components.

Table I

In vitro studies on the potential antiviral effects and mechanisms of garlic-derived components.

First author/s, year	Bioactive compound	Virus studied and model	Key findings	Proposed mechanism of action	(Refs.)
Klenk et al, 2008	Allicin	Influenza A (H1N1, H3N2 and H9N2); MDCK cells	Markedly reduced viral titers and CPE. Showed direct virucidal activity.	Direct virucidal effect: Disrupted the integrity of the viral envelope and key proteins. Inhibited viral replication: May interfere with viral polymerase function. Immuno-modulation: Induced expression of anti-viral cytokines.	(31)
Petrovska and Cekovska, 2010; Jakobsen et al, 2012	Ajoene	HCMV; HHV-1; MRC-5 cell	Potently inhibited viral replication. Showed synergistic effects with standard antivirals (ganciclovir and acyclovir).	Blocked viral entry and cell-cell transmission, primarily by targeting the integrin/NF-κB signaling pathway. Inhibited late stages of replication such as viral assembly and egress. Induced cellular autophagy: This autophagic response was	(27,28)
Tsai et al, 1985; Borlinghaus et al, 2021	DATS/DADS	HCV; Huh7.5 cells; influenza virus; MDCK cells	Suppressed HCV RNA replication and infectious particle production. Protected cells from influenza-induced CPE.	harnessed to degrade viral components. Induced HO-1 expression and activity: This antioxidant enzyme created an anti-viral state in the cell. Direct virucidal activity.	(29,30)
Rouf et al, 2020	Allicin and garlic extract	HRV; human bronchial epithelial cells (BEAS-2B)	Reduced viral RNA load and cytokine release (IL-6 and IL-8). Prevented virus-induced barrier dysfunction.	Immunomodulation: Suppressed virus-induced pro-inflammatory responses and oxidative stress. Preserved epithelial barrier integrity by preventing tight junction disruption.	(1)
Thuy et al, 2020	Garlic extract	SARS-CoV-2; Vero E6 cells	Showed dose-dependent inhibition of SARS-CoV-2 replication.	Direct virucidal activity: Incubation with the extract inactivated viral particles. Inhibited viral entry: May interfere with spike protein binding to the ACE2 receptor.	(32)
Tatarintsev et al, 1992	Saponins (from garlic)	HSV-1 and HSV-2; Vero cells	Exhibited strong inhibition of viral adsorption and penetration into host cells.	Direct virucidal effect: Interacted with the viral envelope, destabilizing it. Blocked viral attachment: May compete with the virus for host cell binding sites.	(33)

[i] DADS, diallyl disulfide; DATS, diallyl trisulfide; HCV, hepatitis C virus; CPE, cytopathic effect; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; HO-1, heme oxygenase-1; ACE2, angiotensin-converting enzyme 2; HCMV, human cytomegalovirus; HHV-1, human herpes virus-1; HRV, human rhinovirus; HSV, herpes simplex virus.

Table II Potential antiviral effects and mechanisms of garlic-derived components based on in vivo studies.

Table II

Potential antiviral effects and mechanisms of garlic-derived components based on in vivo studies.

First author/s, year	Garlic-derived preparation	Virus	Study model	Key antiviral effects	Proposed mechanisms	(Refs.)
Nantz et al, 2012	AGE	Influenza A (H1N1) virus	Mice	Reduced mortality; less severe lung pathology; decreased lung viral titers.	Enhanced cellular immunity: Increased activation and cytolytic activity of NK cells and γδ-T cells in the lungs. Immunomodulation: Modulated cytokine production.	(34)
Guo et al, 1993	Allicin	CMV	Mice	Increased survival rate; reduced viral load in the salivary glands; protected against splenic atrophy.	Immunoenhancement: Reversed the virus-induced suppression of NK cell activity. Modulated cytokine expression (increased IL-2 and IFN-γ expression, as well as decreased IL-10 expression).	(35)
Weber et al, 1992	Ajoene (a stable derivative)	Influenza A (H1N1) virus	Mice	Reduced lung virus titers	Altered viral entry: Shown in vitro to interfere with the early stage of the viral life cycle, potentially by disrupting viral fusion. The in vivo effect is perhaps a combination of direct antiviral action and immunomodulation.	(21)
Fadlalla and Bakhiet, 2010	Fresh garlic clove extract	NDV	Chickens	Enhanced humoral immune response; increased antibody titers against NDV post-vaccination.	Immunomodulation: Acting as an immunostimulant/adjuvant, potentiating the immune response to vaccines.	(36)
Choi and Park, 2012	Garlic essential oil	PRRSV	Pigs	Improved average daily weight gain; reduced lung lesions and viral load in serum.	Immunomodulation: Increased CD4+/CD8+ T cell ratio; modulation of cytokine production.	(37)

[i] CMV, cytomegalovirus; NDV, Newcastle disease virus; PRRSV, porcine reproductive and respiratory syndrome virus; AGE, aged garlic extract; NK, natural killer.

Table III Summary of RCTs investigating garlic-based interventions in viral infection management.

Table III

Summary of RCTs investigating garlic-based interventions in viral infection management.

First author/s, year	Design and population	Garlic intervention	Control	Key findings	Limitations	(Refs.)
Josling, 2001	RCT, parallel groups; 146 healthy adults (mean age, 52 years)	Garlic supplement (allicin), 1 capsule/day for 8 days	Placebo	Marked reduction in cold/flu incidence (24 vs. 65 cases). Shorter symptom duration in garlic group.	Self-reported symptoms. Whole garlic extract, not purified allicin.	(49)
Andrianova et al, 2003	Two-phase RCT; phase I: 640 children (6-17 years); phase II: 115 children (10-12 years)	Garlic tablets, 300-600 mg/day for 150 days	Placebo	Phase II: 50% lower risk of ARVI (RR=0.50). Milder disease course in garlic group	Pediatric population only. Sustained-release formulation used.	(38)
Nantz et al, 2012; Percival, 2016	RCT, parallel groups; 120 healthy adults (mean age, 26 years)	AGE, 2.56 g/day for 90 days	Placebo	A 61% reduction in cold/flu severity. Enhanced NK cell and γδ-T cell function.	Immune markers measured; no viral load data.	(20,34)
Kenawy et al, 2014	RCT, parallel groups; 50 patients with warts (mean age, 25 years)	LGE, applied topically twice daily for 28 days	Saline	A 96% complete clearance of warts. Increased serum TNF-α levels.	Non-randomized design in part. Small sample size.	(39)
Lee et al, 2012	RCT, 4-arm dose-response; 79 patients with chronic hepatitis	DDB and garlic oil capsules (25 + 50 mg), 2-6 caps/day for 42 days	Placebo	Decreased ALT/AST levels. Reduced HBV DNA levels in combination group.	Open-label design. Garlic oil composition variable.	(40)
Hiltunen et al, 2007	RCT, parallel groups; 52 patients (mean age, 38 years)	Intranasal cellulose and PGE spray, once daily per nostril	Cellulose only	Lower respiratory infection incidence (OR=0.30).	Physical barrier mechanism, not direct antiviral.	(41)
Mousavi et al, 2018	RCT, split-body design; 35 men with genital warts (mean age, 33 years)	10% garlic extract, topical application vs. cryotherapy	PEG base	Garlic: 93% clearance vs. cryotherapy: 73% clearance. Lower recurrence with garlic.	Split-body design limits blinding.	(42)
Gołebiowska-Wawrzyniak et al, 2005	RCT, parallel groups; 30 immunodeficient children (3-15 years)	Inosiplex and garlic extract (50 mg/kg/day), for 10 days	Garlic extract only	Enhanced CD3+/CD4+ T cell counts Clinical improvement in viral infections.	Small sample size. Combined immuno-modulator intervention.	(43)

[i] PEG, polyethylene glycol; AGE, aged garlic extract; LGE, lipid garlic extract; DDB, dimethyl-4,4'-dimethoxy-5,6,5',6'-dimethylene dioxybiphenyl-2,2'-dicarboxylate; PGE, powdered garlic extract; ARVI, acute respiratory viral infection; RR, relative risk; NK, natural killer; HBV, hepatitis B virus; ALT, alanine aminotransferase; AST, aspartate aminotransferase; OR, odds ratio; RCT, randomized controlled trial.

Previous research has broadened the general understanding of the therapeutic potential of allicin beyond its direct antiviral activity. Investigations have been increasingly exploring the synergistic effects between allicin and conventional antiviral drugs to enhance treatment efficacy and combat the emergence of drug-resistant viral strains (33,47,48). Furthermore, a number of epidemiological and dietary studies have indicated that regular intake of garlic, a primary source of allicin, may be associated with a lower incidence and severity of viral respiratory infections, including the common cold (primarily caused by rhinoviruses, coronaviruses and respiratory syncytial virus) and influenza (34,49,50). Due to its multi-faceted mechanism of action and favorable safety profile, allicin represents a compelling candidate for use in complementary antiviral regimens. However, comprehensive clinical trials are necessary to determine its safety, optimal dosing and long-term benefits in therapeutic applications.

The present review aims to summarize the latest evidence on the clinical potential of allicin in antiviral therapy, discussing progress in novel delivery systems and synergistic drug combinations, and outlining future directions for developing allicin-based antiviral strategies. With continued investigation, allicin is poised to become a valuable natural therapeutic agent for improving the management of viral infections.

2. Methods

In the present study, literature regarding the antiviral traits and delivery methods of allicin was systematically searched, concentrating on three areas: i) The compound itself (‘allicin’ and ‘garlic extract’); ii) its biological activity (‘antiviral’ and ‘virus inhibition’); and iii) its technological applications (‘nanoparticle’ and ‘drug delivery’). Comprehensive searches were conducted across the PubMed (https://pubmed.ncbi.nlm.nih.gov/), Embase (www.embase.com) and Web of Science (https://www.webofscience.com) databases. The reference lists of the identified articles were also manually checked to ensure that all relevant studies were included. Original research articles investigating the antiviral activity, mechanisms, delivery systems and pharmacokinetics of allicin were included, while non-English publications, studies lacking allicin characterization and non-research articles (such as editorials) were excluded. Priority was given to studies directly addressing the antiviral mechanisms or advanced formulations of allicin, while relevant reviews and foundational papers were also considered to provide broader context.

3. Chemistry and pharmacokinetics

Allicin (diallyl thiosulfinate), the principal bioactive agent derived from garlic, is not intrinsically present in intact cloves. Its formation is triggered by mechanical disruption (crushing or cutting), which initiates an enzymatic process mediated by alliinase (51). This enzyme catalyzes the conversion of the stable precursor alliin (S-allyl-L-cysteine sulfoxide) into allyl sulfenic acid. Subsequently, two molecules of allyl sulfenic acid spontaneously condense to form allicin, a reaction that occurs almost instantaneously and releases the characteristic pungent odor of fresh garlic (52). Chemically, allicin is defined by a thiosulfinate group (S+-S-) and two allyl moieties, with the molecular formula C6H10OS2 (52). A key challenge in its therapeutic use, particularly in antiviral applications, is its inherent chemical instability (53). Allicin is highly reactive and rapidly degrades into a number of oil-soluble sulfur compounds, including ajoene, dithiins and diallyl polysulfides (54). This underscores the critical need for advanced stabilization and delivery strategies to fully harness the antiviral potential of allicin.

The pharmacokinetic profile of allicin is characterized by rapid absorption and extensive metabolism. Upon oral administration, it is readily absorbed from the gastrointestinal tract; however, its high reactivity leads to rapid metabolic conversion (51). Given that allicin is metabolized quickly and extensively before it enters the bloodstream, very little of the ingested dose reaches systemic circulation in its intact form. Lawson and Hunsaker (55) reported that the relative bioavailability of allicin from garlic supplements ranges from 36 to 111% depending on formulation, with values >100% indicating higher absorption than the reference standard used in the study. A radiolabeling study in rats estimated ≥65% absorption of allicin-derived material, although unchanged allicin was absent from urine, confirming extensive presystemic metabolism (56). This low and unpredictable bioavailability is a key barrier to its use as a medicine (51). Evidence has indicated that allicin can permeate cell membranes to exert its biological effects, including intracellular antiviral actions, within infected host cells (57). A notable challenge in pharmacokinetic analysis is the rapid decomposition of the compound, which has limited the development of reliable methods for its direct quantification in human plasma (22). Allicin is not present in intact garlic cloves but is formed upon tissue disruption. Within the intact garlic clove, the stable precursor alliin is stored in the cytoplasm, while the enzyme alliinase is compartmentalized within vacuoles (58,59). Mechanical damage from crushing or cutting brings these components into contact, initiating enzymatic catalysis. Alliinase rapidly converts alliin to allyl sulfenic acid, which spontaneously condenses to form allicin (46,60). Allicin itself is an unstable intermediate that undergoes spontaneous decomposition into various bioactive sulfur-containing metabolites, including DADS, DATS, ajoene, vinyldithiins and S-allyl-cysteine (18,61,62). These metabolites, particularly DADS, DATS, ajoene and vinyldithiins, are considered to markedly contribute to the observed antiviral effects of garlic-derived preparations (1) (Fig. 1). Investigations in rodent models have demonstrated that these metabolites, particularly the lipophilic 1,2-vinyldithiin, exhibit prolonged detectability in serum and tissues such as fat and kidneys for ≤24 h, suggesting a potential for sustained antiviral activity (56,63).

Figure 1 Biochemical pathway of organosulfur compound formation in crushed garlic. DADS, diallyl disulfide; DATS, diallyl trisulfide; SAC, S-allylcysteine.

Following its rapid metabolism, primary derivatives of allicin, including DADS and allyl methyl sulfide (AMS), enter systemic circulation (64). These sulfur-bearing metabolites are subsequently processed in the liver through phase I and II metabolic reactions, such as oxidation and glucuronidation, being ultimately eliminated through renal excretion and exhalation (63). Distribution studies utilizing radiolabeling techniques have revealed that these organosulfur compounds accumulate in a number of key tissues, including the liver, lung parenchyma and respiratory tract mucosa, exhibiting a particular affinity for cartilage-rich areas (56,63). The preferential accumulation of allicin-derived compounds in respiratory tissues supports their potential use against respiratory viral infections (56).

Research has indicated that allicin can modulate key drug metabolism pathways, primarily through interactions with cytochrome P450 (CYP) enzymes. Specifically, allicin has been shown to inhibit the activity of CYP2C19, a mechanism that could potentially elevate systemic levels of co-administered antiviral drugs metabolized by this enzyme, including nelfinavir (an HIV protease inhibitor) and certain anti-hepatitis C virus agents such as dasabuvir (65,66). By contrast, allicin exhibits minimal inhibitory activity against CYP3A4, indicating a degree of enzymatic selectivity in its drug interaction profile (65,66). Understanding these inhibitory effects is key in predicting and managing potential herb-drug interactions in patients receiving allicin-containing supplements alongside specific antiviral regimens that are substrates for CYP2C19.

Clinical investigations into garlic supplements have revealed notable variability in the oral bioavailability of allicin, a key determinant for its systemic antiviral efficacy (55,62,67). This variability is heavily influenced by pharmaceutical formulation and concomitant food intake. For example, the bioavailability from enteric-coated preparations can vary, but is markedly diminished when administered with high-protein meals, perhaps due to prolonged gastric retention (62). Collectively, these factors contribute to the overarching challenge of achieving predictable and effective systemic concentrations of intact allicin following oral administration, severely constraining its reliable clinical translation (68). The pharmacokinetic profile and systemic exposure of allicin-derived metabolites are commonly monitored by quantifying AMS in exhaled breath and urine, serving as a practical surrogate for assessing the handling of these bioactive compounds by the body (62). Understanding how formulation, food intake and metabolic conversion affect allicin bioavailability is essential for designing dosing regimens that achieve therapeutically relevant concentrations in vivo (55,67).

The metabolic fate of allicin involves its rapid conversion into numerous organosulfur metabolites, which can be detected in biological fluids and exhaled breath, providing insights into its systemic distribution and bioavailability (62). Both animal and human studies have determined that allicin is unstable and rapidly metabolized, leading to poor bioavailability (55,56,67,69). To overcome the inherent instability of allicin, research efforts have been directed toward advanced delivery platforms. Nanotechnology has emerged as an important strategy to address these limitations, leading to the development of allicin-encapsulating nanoparticles, liposomes and other carrier systems. These advanced delivery platforms are designed to shield the labile compound from premature degradation and facilitate its targeted delivery to sites of viral infection in a therapeutically active form (23,26). For example, encapsulating allicin within chitosan-based nanocarriers has been shown to enhance its stability, enable a sustained release profile, and consequently, augment its in vivo antiviral efficacy in preclinical studies (70-72). Parallel strategies include prodrug designs, where stable biosynthetic precursors are administered and subsequently converted into active allicin in situ (73-75). These innovative approaches collectively address the primary pharmacokinetic limitations of allicin, namely, its instability, low oral bioavailability and pungent odor, thereby refining its profile as a more viable candidate for clinical development against viral pathogens.

4. Nano-delivery strategies to overcome the limitations of allicin

Although allicin exhibits strong antiviral activity in laboratory studies, its clinical development is limited by physicochemical hurdles, including instability and poor bioavailability (55,56). The extreme chemical instability of the compound in biological environments, coupled with rapid metabolism and poor bioavailability, severely limits its therapeutic utility (23,24,76). Nanotechnology offers a promising solution to close this divide between laboratory results and real-world medical use (77,78). Researchers have been developing sophisticated nanoscale delivery systems to protect allicin from degradation, control its release kinetics, enhance its solubility and bioavailability, and potentially direct it towards specific sites of viral infection, thereby maximizing therapeutic efficacy while minimizing systemic side effects (23,24,75,79).

Design and fabrication of nanocarriers for allicin

Selection of the right nanocarrier is key, and depends on both how the drug will be administered and on the properties of allicin itself. A number of systems have shown potential. Lipid nanoparticles, such as solid lipid nanoparticles (SLNs) and nanostructured lipid carriers, use body-friendly lipids to create a protective shell surrounding the water-repelling allicin (26,80). This shield prevents degradation and allows the drug to be released slowly over time (81). Liposomal structures, characterized by their dual-layer phospholipid composition, can harbor allicin within their lipid membranes, isolating it from aqueous biological environments (23). Among the polymeric options, biodegradable poly(lactic-co-glycolic acid) (PLGA) particles permit fine-tuned release kinetics by adjusting polymer properties, such as molecular weight, lactic-to-glycolic acid ratio and copolymer composition, making them ideal for extended therapeutic action (82,83). Chitosan-based nanoparticles adhere well to mucosal surfaces and help drugs penetrate tissues. This makes them particularly promising for treating respiratory viral infections (84,85). Nanoemulsions have also been studied to improve how well allicin dissolves and is absorbed in the gut (24,86).

Production, analysis and stability enhancement

Development of these nanoformulations requires reliable production techniques and detailed physical characterization. Standard methods comprise high-shear homogenization for lipid-based carriers, solvent evaporation processes for polymer-based systems and high-energy dispersion for nanoemulsions (81,87). Detailed analysis is key as it ensures the product is consistent and helps predict how it will perform in the body. Important parameters to consider include particle size and size distribution, which determine circulation time in the bloodstream, cellular uptake efficiency and biodistribution, with an optimal size range of 80 to 200 nm typically reported for intravenous delivery (81,88). Surface electrical properties (ζ potential) influence particle stability and their engagement with biological surfaces (84). The most important measures include encapsulation success and drug payload, which indicate how effectively allicin is incorporated. Studies have shown that allicin in SLNs can achieve encapsulation efficiencies >75%. This greatly improves its stability, protecting the majority of the compound in gut-like conditions where free allicin would otherwise break down quickly (26,86).

Enhanced antiviral performance of nanoformulated allicin

Comparative studies across in vitro and in vivo models have robustly demonstrated the superior antiviral efficacy of nano-encapsulated allicin compared with its free form (77,89). This improvement is primarily attributed to the protective effect of nanocarriers on the fragile allicin molecule. For example, engineered delivery systems, such as whey protein isolate/chitosan (WPI/CS) complexes and zein-sodium caseinate nanoparticles, have been shown to markedly enhance the stability and encapsulation efficiency of allicin, creating a reservoir of the active compound shielded against rapid degradation in physiological environments (90,91). This protection directly translates into stronger and more sustained intracellular antiviral activity (92).

In vitro evidence has further demonstrated this advantage. In nanomedicine, it is well-established that encapsulation can notably improve the cellular uptake and bioavailability of poorly soluble or unstable drugs, thereby enhancing their pharmacological activity (93-96). This principle has been validated across numerous drug classes, including antitumor agents and antibiotics (97). Furthermore, the potential of nano-encapsulation to boost the antiviral potency of bioactive compounds such as allicin is supported by precedents with other molecules. For example, nanoformulations have shown efficacy in overcoming the poor solubility and stability of curcumin and resveratrol, leading to marked improvements in their in vitro and in vivo bioactivity (98). This evidence provides a compelling rationale for applying analogous strategies for allicin. The principles demonstrated by WPI/CS and zein-caseinate systems, including efficient encapsulation, protection from degradation and controlled release, underpin these outcomes, as stable encapsulation is a prerequisite for sustained intracellular delivery and action (90,91).

These laboratory-based advantages, including enhanced stability, prolonged circulation and improved cellular uptake, have been consistently corroborated in animal infection models (78). The improved in vivo outcomes of nanoformulated allicin are attributed to the enhanced permeability and retention (EPR) effect, a passive targeting mechanism whereby nanoparticles accumulate selectively at sites of inflammation or infection due to leaky vasculature and impaired lymphatic drainage (99,100). This EPR-like phenomenon has been directly demonstrated in infectious disease models, including tuberculosis granulomas (101), confirming its relevance for targeted antimicrobial delivery (102). As a key principle in nanoparticle drug delivery to diseased sites, the EPR effect, a well-documented concept in tumor biology and infectious inflammation, facilitates the passive accumulation of nano-sized carriers at sites with leaky vasculature (101-104). This principle has been successfully leveraged to improve the delivery to sites of infection and inflammation and efficacy of numerous nanomedicines, including liposomal amphotericin B (AmBisome®) for fungal infections, liposomal antibiotics for intracellular bacteria and polymeric nanoparticles for tuberculosis treatment (105-107). Therefore, designing allicin nanoformulations represents a logical approach to enhance its targeting and accumulation at viral infection sites. The improved therapeutic results can be attributed to two main factors: i) The nanocarriers stabilize allicin during systemic circulation; and ii) they utilize mechanisms such as the EPR effect to promote its accumulation at the site of infection (90,101).

Improved pharmacokinetics and tissue distribution

Nanocarriers effectively address the core pharmacokinetic challenge of allicin, namely its low oral bioavailability, by enhancing its stability and absorption (23,79). Nanoparticulate systems have been demonstrated to enhance the oral bioavailability of challenging drugs by protecting them from gastrointestinal degradation and facilitating absorption through lymphatic transport (108). This strategy has been extensively validated, including through the use of curcumin, the oral bioavailability and therapeutic efficacy of which have been increased by numerous orders of magnitude through nanoencapsulation, markedly transforming its translational potential (109-111). Such successful case studies form a compelling precedent for addressing the analogous delivery challenges posed by allicin (23,79,112). Specifically, encapsulating allicin within delivery systems such as nanoemulsions has been shown to markedly enhance its intestinal absorption and systemic exposure levels (1). This improvement in bioavailability is key in realizing the full spectrum of documented health benefits of allicin, including its antimicrobial and antioxidant properties (23).

With regard to systemic administration, the use of nanocarriers, particularly those coated with polyethylene glycol (PEG), is an effective strategy to prolong the circulation time and favorably alter pharmacokinetic profiles, a concept well-documented in the literature (113-116). PEGylation is a well-established technique to evade immune clearance, as evidenced by its success in numerous U.S. Food and Drug Administration-approved nanomedicines, including Doxil® (pegylated liposomal doxorubicin), Oncaspar® (pegylated L-asparaginase), Neulasta® (pegylated granulocyte colony-stimulating factor), Pegasys® (pegylated interferon alfa-2a) and Cimzia® (pegylated antibody fragment) (117-119). Consistent with this, allicin packaged in PLGA nanoparticles exhibits prolonged detectability and increased systemic exposure compared with the free molecule, with studies reporting an up to 4.2-fold higher area under the curve and extended half-life for various drugs encapsulated in PLGA nanoparticles (120,121).

Beyond enhancing systemic levels, nanocarriers can redirect drug distribution within the body. Nanoparticles can be engineered to achieve modified biodistribution, leading to increased drug accumulation in target tissues such as the liver, spleen and sites of inflammation or infection, thereby improving the therapeutic index (122). Active targeting strategies employing specific ligands further validate the ability to direct nanoformulations to particular cell types, a principle readily applicable to targeting infected tissues (123). Investigations using tracking methods have shown that nanoparticles can promote the preferential accumulation of allicin in organs with active immune activity or altered vascular permeability, such as the lungs and liver, which are common sites of viral pathology (87,124,125). This redirected distribution not only elevates drug concentrations at sites of infection but also reduces the risk of off-target effects, including toxicity to healthy tissues such as the heart, kidneys and bone marrow, as well as minimizing non-specific immune activation and inflammation (126,127).

Conclusions

In conclusion, the strategic application of nanoscale drug delivery technologies represents a marked advancement in elucidating the therapeutic potential of allicin (79). Encapsulation of this chemically unstable compound within rationally designed nanocarriers has enabled improved stabilization, enhanced efficacy, and optimized pharmacokinetic behavior and favorable tissue targeting (71,128). Collectively, current evidence indicates that nanodelivery systems constitute a key strategy in transforming allicin from a promising natural compound into a clinically viable therapeutic agent (23,79). Future research is expected to focus on the development of more sophisticated delivery platforms, including stimulus-responsive nanocarriers capable of releasing allicin selectively under pathological conditions such as reduced pH, as well as actively targeted systems functionalized with ligands that recognize virus-infected cells (128). The continued integration of advanced materials engineering with the broad-spectrum antiviral properties of allicin holds promise for the development of novel effective antiviral therapies.

5. Allicin as a natural antiviral therapeutic agent

Viral infections continue to pose a notable and evolving threat to global public health, with both emerging and re-emerging pathogens contributing to morbidity and mortality worldwide (44). The limitations of existing antiviral therapies, including narrow-spectrum activity, the emergence of drug-resistant viral strains and high treatment costs, underscore the urgent need for novel antiviral agents (129). In this context, scientific attention has been increasingly directed toward natural products as valuable resources for drug discovery. Allicin, a bioactive organosulfur compound formed when garlic tissue is crushed or damaged, has attracted considerable interest due to its broad-spectrum antimicrobial properties, with increasing evidence supporting its antiviral potential (1,3,52,130).

As illustrated in Fig. 2, garlic-derived organosulfur compounds, particularly allicin, exhibit multifaceted antiviral mechanisms. These include direct inactivation of viral particles and interference with viral entry, replication and assembly (131,132). Molecular docking studies have further demonstrated that allicin and its derivatives (such as diallyl sulfide, diallyl disulfide, diallyl trisulfide and ajoene) inhibit key viral enzymes, including the SARS-CoV-2 3C-like protease and RNA-dependent RNA polymerase, thereby suppressing viral replication (133-135). Additionally, allicin modulates host inflammatory responses by suppressing the NLR family pyrin domain containing 3 inflammasome pathway, reducing excessive inflammation and associated tissue damage (136). These combined direct antiviral and immunomodulatory actions contribute to the broad-spectrum therapeutic potential of allicin against viral infections (131,132). Notably, the antiviral effects of allicin exhibit a clear dose-response relationship. For example, Weber et al (21) demonstrated concentration-dependent virucidal activity against herpes simplex virus types 1 and 2, providing classic pharmacological evidence regarding the dose-dependent antiviral action of allicin (21). Mechanistic studies have suggested that allicin exerts context-dependent effects on the cellular redox status. In virus-infected cells, allicin induces oxidative stress through S-thioallylation of protein thiols and glutathione depletion, leading to redox-mediated alterations that promote the degradation of viral components and create an unfavorable environment for viral replication (46,57,137). By contrast, in uninfected cells and tissues, allicin and its metabolites activate the nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidant pathway, enhancing cellular antioxidant defenses and reducing oxidative stress and inflammation, thereby mitigating virus-associated tissue damage (21,33,57,138-143) (Fig. 2; Table IV). This dual mechanism, selective pro-oxidant action in infected cells coupled with cytoprotective antioxidant effects in healthy tissues, contributes to the therapeutic selectivity of allicin against viral infections (137). In addition, allicin has been shown to modulate host cell signaling pathways, including the Nrf2 pathway, which serves an important role in regulating cellular antioxidant defenses. Activation of this pathway by allicin induces antioxidant enzymes that create an intracellular environment unfavorable for viral replication, thereby suppressing viral propagation (44,138,144). Notably, such modulation occurs within an optimal concentration range rather than in a linear manner, as emphasized in reviews of the immunomodulatory effects of garlic-derived compounds (145-147). Furthermore, allicin has been reported to act synergistically with conventional antiviral drugs in certain contexts, including enhanced inhibition of respiratory syncytial virus when combined with moroxydine and α-interferon, potentially enhancing therapeutic efficacy while reducing the required drug dosage and associated toxicity (4,148). This synergistic effect may additionally contribute to minimizing adverse effects and limiting the emergence of drug-resistant viral strains (149,150).

Figure 2 Proposed multifaceted antiviral and protective mechanisms of allicin. ACE2, angiotensin-converting enzyme 2; NK, natural killer; ALT, alanine aminotransferase; AST, aspartate aminotransferase; NLRP3, NLR family pyrin domain containing 3; 3CLpro, 3C-like protease; RdRp, RNA-dependent RNA polymerase.

Table IV Summary of the main antiviral mechanisms of garlic-derived compounds.

Table IV

Summary of the main antiviral mechanisms of garlic-derived compounds.

First author/s, year	Mechanism category	Pathway/target involved	Primary action	Core antiviral function	(Refs.)
Weber et al, 1992	Direct antiviral action	Viral particles/enzymes (such as neuraminidase)	Inhibition/inactivation	Blocking numerous stages of the viral life cycle.	(21)
Miron et al, 2000; Nan et al, 2021	Host cellular state modulation	Oxidative and ER stress	Induction	Creating an unfavorable environment for viral replication; degrading viral components.	(57,140)
Zeng et al, 2013; Zhang et al, 2022		Nrf2 signaling pathway	Activation	Enhancing cellular antioxidant defense, maintaining homeostasis	(141,142)
Tatarintsev et al, 1992; Bouyahya et al, 2025	Host immunity and fate regulation	NF-κB pathway	Inhibition	Limiting viral exploitation of host resources; mitigating excessive inflammation.	(33,143)

[i] ER, endoplasmic reticulum; Nrf2, nuclear factor erythroid 2-related factor 2.

In addition to allicin, other garlic-derived organosulfur compounds also exhibit broad-spectrum antiviral activity through diverse mechanisms. Alliin, the biosynthetic precursor of allicin, has been shown to suppress viral replication in infected cells while exhibiting minimal cytotoxicity toward uninfected host cells, suggesting a degree of selectivity in its antiviral action (1). This selective activity implies a favorable therapeutic window, a key principle of dose-response pharmacology (3). Comparative analyses, including those summarized by Ankri and Mirelman (3), indicate that the concentrations required for antimicrobial (including antiviral) effects are often markedly lower compared with those associated with toxicity in mammalian cells, thereby defining a beneficial selective index.

Specifically, this selectivity translates into a favorable therapeutic window. In vitro studies have demonstrated that allicin exhibits concentration-dependent antiviral activity with a quantifiable safety margin (21,132,137). Effective concentrations against numerous viruses are often observed in the low micromolar range, whereas cytotoxic concentrations are notably higher. As a result, reported selectivity indices frequently exceed a score of 3, as shown in comparative bioactivity analyses (3,21). However, this therapeutic window is not fixed and may vary depending on the viral species, host cell type and experimental conditions (21). Notably, translating in vitro potency into safe and effective human dosing requires systematic investigation, as achieving and maintaining therapeutic plasma or tissue concentrations in vivo involves complex pharmacokinetic and bioavailability factors that remain incompletely characterized (51).

DADS, a stable transformation product of allicin, has been shown to enhance host antiviral defenses by activating the Nrf2 signaling pathway. This upregulates a network of antioxidant and cytoprotective genes that can restrict viral replication (141). Similarly, DATS interferes with numerous stages of the viral life cycle, potentially through disruption of viral entry and assembly processes (44). The antiviral activity of DATS and related compounds is explicitly concentration-dependent, with efficacy increasing sharply across a narrow dose range in experimental models (151). Furthermore, the induction of caspase-3 and caspase-8 activity in virus-infected cells indicates that these compounds can promote apoptosis of infected cells, thereby limiting viral spread (57). This pro-apoptotic effect itself requires a threshold concentration to initiate the apoptotic cascade, reflecting a key principle of dose-response pharmacology (57). In addition, secondary metabolites such as S-allylmercaptocysteine and S-allylcysteine contribute to overall antiviral efficacy by inhibiting viral replication and facilitating the clearance of infected cells (21).

The proposed mechanism underlying the antiviral activity of allicin is summarized in Fig. 2. Following cellular uptake in virus-infected cells, allicin primarily induces intracellular oxidative stress through the generation of reactive oxygen species, which can promote degradation of viral components (57). A key aspect of its antiviral action involves modulation of host cell signaling pathways important for viral replication. Allicin has been shown to influence the NF-κB pathway, a central regulator of inflammation and cell survival that is frequently exploited by viruses (131,152). In addition, allicin affects MAPK signaling cascades, which viruses commonly manipulate to establish a favorable intracellular environment (131,153). Collectively, these mechanisms, including induction of oxidative stress and disruption of pro-viral signaling networks, result in inhibition of viral replication and facilitate elimination of infected cells, potentially through enhanced caspase-mediated apoptosis (154,155).

Beyond modulation of the cellular redox state, allicin activates key host defense signaling pathways, such as the ERK/MAPK pathway, thereby promoting an intracellular environment unfavorable for viral replication (156). Unlike the aforementioned direct oxidative stress mechanisms, which degrade viral components through chemical modification, these signaling pathways regulate immune gene expression and cellular antiviral responses (132,156). Studies have shown that allicin stimulates the JNK and p38 MAPK signaling cascades, both of which serve important roles in initiating intrinsic antiviral responses (19,140,156). Activation of these pathways promotes the upregulation of immunomodulatory receptors and facilitates caspase activation, which are processes that contribute to the programmed elimination of virus-infected cells (30). As a result, viral production and spread are effectively curtailed (1). This multifaceted engagement of host signaling networks highlights the ability of allicin to disrupt the viral life cycle through both direct antiviral effects and indirect host-mediated mechanisms.

Allicin further combats viral infection by inducing programmed cell death in infected host cells through a number of molecular pathways. This process includes disruption of mitochondrial integrity, leading to the cytosolic release of pro-apoptotic factors that subsequently activate key effector enzymes (57). In addition, allicin can induce endoplasmic reticulum stress in infected cells, a mechanism known to interfere with viral protein synthesis and folding. This disruption contributes to suppression of viral replication and promotes clearance of infected cells (26). Collectively, these complementary mechanisms enhance overall antiviral efficacy by eliminating cellular niches that support viral replication. To clarify how these multifaceted actions operate in concert, the core antiviral pathways and mechanisms of allicin are summarized in Table IV (21,33,57,140-143).

Beyond its direct antiviral effects, allicin may also serve a protective role in mitigating virus-associated tissue damage and modulating the host immune response. For example, activation of cellular defense pathways such as the Nrf2-mediated antioxidant response has been shown to reduce oxidative stress and inflammatory injury in experimental models of viral hepatitis, thereby contributing to liver protection (23). In addition, the immunomodulatory properties of allicin suggest potential benefits in attenuating excessive inflammatory responses commonly observed in severe viral infections (19). Although numerous in vivo and preclinical studies support these protective effects (30,137,138), further clinical investigations are required to determine their relevance and applicability in the management of human viral diseases (157,158). Overall, available evidence underscores the role of garlic-derived compounds in modulating inflammatory profiles in chronic pathological conditions.

6. Safety aspects

Careful evaluation is warranted when considering the safety profile of allicin in relation to its application as an antiviral therapeutic agent. Despite garlic having a long history of dietary use, the potent biological activity of allicin necessitates thorough assessment of potential adverse effects (22,159). A major limitation in current safety evaluations is the heavy reliance on animal toxicology studies, accompanied by a lack of comprehensive human safety trials and long-term surveillance data needed to fully characterize risks under therapeutic conditions (160,161).

Clinical observations indicate that high-dose allicin supplementation may cause gastrointestinal discomfort, including nausea, heartburn and diarrhea, as well as systemic effects such as headache, tachycardia and mild hypotension in susceptible individuals (49). However, existing human data are largely derived from efficacy-oriented studies with limited safety monitoring periods. These studies lack the systematic, longitudinal design required to detect rare or delayed adverse events (22,160,162). Consequently, there is a clear need for prospective safety studies specifically designed to evaluate the risk profile of allicin in defined patient populations across extended treatment durations.

Experimental studies have demonstrated a clear dose-dependent toxicity profile for allicin (163,164). At low to moderate doses, allicin enhances antioxidant capacity in animal models. By contrast, excessive administration (for example, 1,000 mg/kg/day in rats) has been associated with hepatorenal toxicity, as evidenced by histopathological alterations in liver and kidney tissues (165). The molecular basis of this differential effect may be attributed to the characteristics of allicin as a reactive sulfur species. Allicin readily penetrates biological membranes and oxidizes intracellular thiols, including glutathione and protein cysteine residues. Such oxidative reactions can induce structural modifications through disulfide bond formation, thereby disrupting normal cellular function and potentially resulting in cytotoxic effects (57).

Chronic high-dose exposure studies have identified additional safety concerns. Prolonged administration of concentrated garlic preparations has been associated with hematological abnormalities, including oxidative hemolysis of erythrocytes, as well as body weight loss and impaired spermatogenesis in rodent models (165,166,167). In addition, toxicological investigations of pulmonary and hepatic systems indicate that sustained consumption of high doses of garlic juice can induce adverse changes in these organs (168,169). Collectively, these findings emphasize the importance of careful dose optimization and duration control in the development of allicin-based antiviral formulations.

Overall, preclinical evidence supports a dose-dependent safety profile for allicin, in which beneficial or neutral effects are observed at lower concentrations [for example, 5-20 mg/kg/day in mice (170) and 15-45 mg/kg/day in rats (171)], whereas sustained exposure to doses exceeding the therapeutic range may result in adverse organ effects, including signs of hepatorenal stress in rodent models (171). Translation of these toxicological findings to human risk assessment requires cautious interpretation due to well-documented interspecies differences in drug metabolism and physiological responses (172). Consequently, a central objective in translational development is to empirically define the human therapeutic window by identifying dose ranges that achieve antiviral efficacy while maintaining an acceptable safety margin. This process necessitates systematic phase I clinical trials designed to characterize pharmacokinetics, assess tolerability and establish the maximum tolerated dose in human subjects (173). Therefore, although existing non-clinical data identify exposure thresholds associated with toxicological risk, definitive demonstration of the safety of allicin at clinically relevant doses must rely on prospective, well-controlled studies in human populations (68).

Beyond the intrinsic toxicity profile of allicin and garlic-derived preparations, their potential to interact with conventional medications represents an additional key safety consideration. The most extensively documented interaction involves anticoagulant and antiplatelet therapies (174-176). Allicin and other garlic organosulfur compounds exhibit antiplatelet activity, perhaps through inhibition of thromboxane synthesis and platelet aggregation. As a result, these compounds may potentiate the effects of anticoagulant and antiplatelet drugs such as warfarin, aspirin and clopidogrel, thereby increasing the risk of bleeding, particularly with high-dose or prolonged garlic supplementation (174,177). Documented interactions between warfarin and concentrated garlic products have been reported in the literature, including cases of elevated international normalized ratios and bleeding events (178-180).

Such inhibition may increase the systemic exposure and toxicity of drugs that are substrates of these enzymes, including CYP2C19 substrates such as proton pump inhibitors (such as omeprazole), antiplatelet drugs (such as clopidogrel) and certain antiviral agents (such as nelfinavir) (65,66). This effect is especially relevant in antiviral therapy, as numerous protease inhibitors used in the treatment of HIV and hepatitis C rely heavily on CYP3A4-mediated metabolism (181). Conversely, evidence has indicated that chronic garlic consumption may induce CYP enzyme activity, underscoring the complexity and dose- and duration-dependent nature of these interactions (182).

In addition, given the reported hypoglycemic effects of garlic supplementation, including reductions in fasting blood glucose and hemoglobin A1c in patients with type 2 diabetes (183,184), and its antihypertensive effects, including modest but significant reductions in both systolic and diastolic blood pressure in individuals with hypertension (185,186), potential interactions with antihypertensive and antidiabetic medications warrant consideration, although supporting clinical evidence remains limited (187). Consequently, for allicin to be safely incorporated into antiviral treatment regimens, particularly as part of combination therapies, careful patient selection, monitoring of coagulation parameters and drug concentrations (when applicable), and clear guidance regarding the use of standardized formulations vs. dietary garlic preparations are key.

7. Conclusion and future perspectives

Allicin, a principal organosulfur compound derived from garlic, exhibits potential as a broad-spectrum antiviral agent based on extensive preclinical research. Its antiviral activity arises from numerous complementary mechanisms, including direct virucidal effects, disruption of viral replication processes and modulation of host cellular signaling pathways.

Current clinical evidence, summarized in Table III, suggests that garlic-based interventions may provide therapeutic benefits for certain viral infections, including reductions in cold/flu incidence and severity, as well as improved clinical outcomes in viral hepatitis and cutaneous warts. However, as shown in Table III, these studies predominantly used multi-component garlic preparations (such as whole extract, aged extract and garlic oil) rather than purified allicin, and exhibited considerable heterogeneity in study design, dosing and clinical endpoints (20,34,38-43,49). This variability highlights a gap between controlled experimental findings and validated clinical application.

Notable progress has been made in overcoming the physicochemical limitations of allicin, particularly through the development of engineered delivery systems such as nanocarriers, which enhance stability and systemic bioavailability. Although these technological advances represent key prerequisites, definitive evidence of antiviral efficacy, optimized dosing regimens and comprehensive safety profiles for purified or formulated allicin in humans must still be established through clinical investigation.

Future research should aim to prioritize clinical validation of these advanced delivery platforms. The most important subsequent steps include conducting phase-appropriate clinical trials using standardized allicin formulations to characterize pharmacokinetics, defining dose-response relationships and assessing safety, including the potential for drug-drug interactions, in relevant patient populations, including individuals with acute viral infections [such as influenza or COVID-19(157)], those at high risk of viral complications [including immunocompromised or elderly patients (188)] and patients receiving concurrent antiviral or other medications that may interact with allicin (188,189). In addition, research efforts should continue to elucidate pathogen-specific mechanisms of action and host-directed immunomodulatory effects.

In summary, allicin represents a scientifically well-established antiviral candidate supported by robust preclinical evidence and emerging, albeit preliminary, clinical observations. Its successful translation into a viable antiviral therapeutic will depend on coordinated research strategies designed to systematically bridge existing evidence gaps through targeted clinical studies and formulation-focused innovation.

Acknowledgements

Not applicable.

Funding

Funding: The present review was supported by the Construction Task Book of Hangzhou Biomedical and Health Industry Development Support Science and Technology Special Project (Phase 14; grant no. 2024WJC135), the Zhejiang Traditional Chinese Medicine Science and Technology Project (grant no. 2023ZL565) and the Construction Fund of Key Medical Disciplines of Hangzhou (grant no. HWB-2025-10).

Availability of data and materials

Not applicable.

Authors' contributions

MJY and ZM conceptualized the study and wrote the original draft of the manuscript. YZ and WZ were involved in the screening, extraction and analysis of the literature data, based on which they designed the figures and tables. QPX and ZM contributed to the writing, review and revision of the manuscript. HMW contributed to the construction of the theoretical framework, the interpretation of data and the critical review of key sections of the manuscript. Data authentication is not applicable. All authors have read and approved the final version of the manuscript.

Ethics approval and consent to participate

Not applicable.

Patient consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

References