S-Allylcysteine

Pharmacology & Research

S-allylcysteine (SAC) is the odourless, water-soluble organosulfur compound that accumulates as garlic is aged, and it is the standardisation marker for aged garlic extract (AGE). Its defining feature separates it from the rest of garlic’s chemistry: unlike allicin, ajoene and the diallyl sulfides — which are reactive, unstable and poorly bioavailable — SAC is chemically stable and highly bioavailable ^{4,1Reference 42002Physical, chemical and biological properties of S-allylcysteine, an amino acid derived from garlicView study →Reference 1Nagae S et al. · 1994Pharmacokinetics of the garlic compound S-allylcysteineView study →}. (It is also distinct from alliin, its oxidised sulfoxide precursor.) That stability makes it both a good research molecule and the reason AGE is standardised to it. Its most-developed pharmacology is preclinical antioxidant and neuroprotective activity via the Nrf2/ARE antioxidant program ^{5,7Reference 52015On the antioxidant, neuroprotective and anti-inflammatory properties of S-allylcysteine: an updateView study →Reference 72015In vitroS-allylcysteine activates the Nrf2-dependent antioxidant response and protects neurons against ischemic injury in vitro and in vivoView study →}. The key honesty point runs through the whole page: the human cardiovascular evidence is for aged garlic extract standardised to SAC, not for isolated SAC — SAC is the measuring stick, not proven to be the active agent.

1. Antioxidant / neuroprotective

SAC’s most-developed application. It scavenges radicals and activates the Nrf2/ARE antioxidant program, raising SOD, catalase and glutathione peroxidase in striatum, cortex and hippocampus, preserving BDNF, and protecting neurons in excitotoxicity, ischemia and mitochondrial-dysfunction models ^{5,7,8Reference 52015On the antioxidant, neuroprotective and anti-inflammatory properties of S-allylcysteine: an updateView study →Reference 72015In vitroS-allylcysteine activates the Nrf2-dependent antioxidant response and protects neurons against ischemic injury in vitro and in vivoView study →Reference 82020S-allylcysteine protects against excitotoxic damage via Nrf2/ARE binding and BDNF preservationView study →} — including protection of brain synaptosomes against 3-nitropropionic-acid injury ^{9Reference 92006AnimalProtective effect of S-allylcysteine on 3-nitropropionic-acid-induced lipid peroxidation and mitochondrial dysfunction in rat brain synaptosomesView study →}; the antioxidant-mechanism reviews consolidate the case ^{6Reference 62012The antioxidant mechanisms underlying the aged-garlic-extract- and S-allylcysteine-induced protectionView study →}.

Gap: entirely preclinical for neurological endpoints — there are no human neurodegeneration or stroke trials of SAC (or AGE) at clinical endpoints, and the effects are shown at injected or high oral rodent doses ^{5,8Reference 52015On the antioxidant, neuroprotective and anti-inflammatory properties of S-allylcysteine: an updateView study →Reference 82020S-allylcysteine protects against excitotoxic damage via Nrf2/ARE binding and BDNF preservationView study →}.

2. Cardiovascular (aged garlic extract)

Aged garlic extract, standardised to SAC as its marker, modestly lowers blood pressure in hypertensives, nudges serum cholesterol, improves endothelial function in men with coronary disease, and slowed subclinical atherosclerosis progression ^{16,18,19Reference 16Ried K et al. · 2016Garlic lowers blood pressure in hypertensive individuals, regulates serum cholesterol and stimulates immunityView study →Reference 182005Aged garlic extract improves endothelial function in men with coronary artery diseaseView study →Reference 192009RCTAged garlic extract supplemented with B-vitamins, folic acid and L-arginine retards the progression of subclinical atherosclerosis: a randomised clinical trialView study →}; a meta-analysis found the blood-pressure benefit significant chiefly above ~1200 mg/day of AGE ^{17Reference 17Saadh MJ et al. · 2024Meta-analysisEffects of aged garlic extract on blood pressure in hypertensive patients: a systematic review and meta-analysisView study →}.

Gap: this human evidence is for the whole aged extract, not SAC in isolation — SAC is the standardisation handle, not proven the active moiety, and the atherosclerosis trial added B-vitamins, folate and L-arginine ^{17,19Reference 17Saadh MJ et al. · 2024Meta-analysisEffects of aged garlic extract on blood pressure in hypertensive patients: a systematic review and meta-analysisView study →Reference 192009RCTAged garlic extract supplemented with B-vitamins, folic acid and L-arginine retards the progression of subclinical atherosclerosis: a randomised clinical trialView study →}.

3. Hepatoprotective

SAC reduced porcine-serum-induced hepatic fibrosis in rats ^{10Reference 102009AnimalS-allylcysteine is effective as a chemopreventive agent against porcine-serum-induced hepatic fibrosis in ratsView study →}, protected HepG2 cells from peroxide injury via Akt/Nrf2/HO-1 ^{11Reference 112018S-allylcysteine alleviates hydrogen-peroxide-induced oxidative injury and apoptosis through Akt/Nrf-2/HO-1 in HepG2 cellsView study →}, and attenuated free-fatty-acid lipogenesis via AMPK ^{12Reference 122013S-allylcysteine attenuates free-fatty-acid-induced lipogenesis in human HepG2 cells through an AMPK-dependent pathwayView study →}; a double-blind RCT of fermented garlic extract lowered elevated GGT in adults ^{20Reference 202017RCTEfficacy and safety of fermented garlic extract on hepatic function: a double-blind, randomised, placebo-controlled trialView study →}.

Gap: mechanistic/animal for the isolate, and the only human liver trial used fermented garlic extract — a related preparation, not isolated SAC ^{11,20Reference 112018S-allylcysteine alleviates hydrogen-peroxide-induced oxidative injury and apoptosis through Akt/Nrf-2/HO-1 in HepG2 cellsView study →Reference 202017RCTEfficacy and safety of fermented garlic extract on hepatic function: a double-blind, randomised, placebo-controlled trialView study →}.

4. Anticancer

SAC induced apoptosis and oxidative cytotoxicity in lung cancer lines (downregulating Nrf2/NF-κB and suppressing PD-L1) ^{14Reference 142021S-allylcysteine induces cytotoxic effects in two human lung cancer cell lines via downregulation of Nrf2 and NF-κB and apoptosisView study →} and inhibited tumour progression and epithelial-mesenchymal transition in an oral-cancer mouse xenograft ^{15Reference 152012AnimalS-allylcysteine inhibits tumour progression and the epithelial-mesenchymal transition in a mouse xenograft model of oral cancerView study →}, with a review cataloguing diverse mechanisms ^{13Reference 132020Garlic-derived bioactive compound S-allylcysteine inhibits cancer progression through diverse molecular mechanismsView study →}.

Gap: no human oncology data at all — effects are in-vitro or a single xenograft, so this is speculative ^{13,15Reference 132020Garlic-derived bioactive compound S-allylcysteine inhibits cancer progression through diverse molecular mechanismsView study →Reference 152012AnimalS-allylcysteine inhibits tumour progression and the epithelial-mesenchymal transition in a mouse xenograft model of oral cancerView study →}.

5. Metabolic

SAC suppressed hepatic lipogenesis in an AMPK-dependent manner in HepG2 cells ^{12Reference 122013S-allylcysteine attenuates free-fatty-acid-induced lipogenesis in human HepG2 cells through an AMPK-dependent pathwayView study →}.

Gap: thin — one cell model that overlaps the hepatoprotective story, with no whole-animal metabolic-endpoint or human data for isolated SAC ^{12Reference 122013S-allylcysteine attenuates free-fatty-acid-induced lipogenesis in human HepG2 cells through an AMPK-dependent pathwayView study →}.

Mechanisms

Target / pathway	Effect	Relevant to
Nrf2/ARE → ↑ SOD, catalase, GSH-Px, HO-1	endogenous antioxidant-enzyme induction	neuroprotection, hepatoprotection
Direct radical/ROS scavenging	↓ lipid peroxidation, mitochondrial protection	excitotoxic and metabolic-stress models
NF-κB modulation	↓ inflammatory signalling; pro-apoptotic in tumour cells	anti-inflammatory, anticancer
AMPK activation	↓ hepatic lipogenesis	metabolic/hepatic
H₂S / NO modulation, endothelial function (AGE context)	vasorelaxation, blood-pressure effect	cardiovascular

Pharmacokinetics

This is SAC’s strongest point of difference from every reactive garlic sulfur compound. It is well absorbed and stable: oral bioavailability is ~64% in mouse, ~89% in rat and ~98% in dog ^{1Reference 1Nagae S et al. · 1994Pharmacokinetics of the garlic compound S-allylcysteineView study →}, with a modern rat/dog study confirming rapid, near-complete absorption ^{2Reference 2Amano H et al. · 2015AnimalMetabolism, excretion and pharmacokinetics of S-allyl-L-cysteine in rats and dogsView study →}. It is odourless, water-soluble and not degraded like allicin, so it is measurable in plasma and tissue — which is precisely why AGE is standardised to it ^{4,3Reference 42002Physical, chemical and biological properties of S-allylcysteine, an amino acid derived from garlicView study →Reference 32025ReviewPharmacokinetics of sulfur-containing compounds in aged garlic extract (review)View study →}. It distributes to plasma, liver and kidney, is partly N-acetylated, and is excreted primarily in the urine as SAC and its N-acetyl metabolite ^{2,1Reference 2Amano H et al. · 2015AnimalMetabolism, excretion and pharmacokinetics of S-allyl-L-cysteine in rats and dogsView study →Reference 1Nagae S et al. · 1994Pharmacokinetics of the garlic compound S-allylcysteineView study →}. In short, unlike most molecules in this collection, SAC’s pharmacokinetics are favourable — the caveat is not absorption but that the human efficacy data still come from the whole extract.

Clinical trials

There are no controlled human trials of isolated SAC. All human data are for aged garlic extract standardised to SAC: reviews and meta-analyses of AGE for blood pressure and cholesterol ^{16,17Reference 16Ried K et al. · 2016Garlic lowers blood pressure in hypertensive individuals, regulates serum cholesterol and stimulates immunityView study →Reference 17Saadh MJ et al. · 2024Meta-analysisEffects of aged garlic extract on blood pressure in hypertensive patients: a systematic review and meta-analysisView study →}, an endothelial-function RCT in coronary-artery-disease men ^{18Reference 182005Aged garlic extract improves endothelial function in men with coronary artery diseaseView study →}, and a subclinical-atherosclerosis RCT (AGE plus B-vitamins/folate/L-arginine) ^{19Reference 192009RCTAged garlic extract supplemented with B-vitamins, folic acid and L-arginine retards the progression of subclinical atherosclerosis: a randomised clinical trialView study →}; a separate RCT of fermented garlic extract reduced GGT ^{20Reference 202017RCTEfficacy and safety of fermented garlic extract on hepatic function: a double-blind, randomised, placebo-controlled trialView study →}. Every clinical claim must be attributed to the extract, with SAC named only as the marker.

Last checked: July 2026.

Toxicity & Safety

SAC has very low toxicity — a genuinely safe compound, markedly less toxic than allicin and its reactive congeners, with a high margin of safety in rodent work (roughly an order of magnitude less toxic than allicin or diallyl disulfide) ^{4,21Reference 42002Physical, chemical and biological properties of S-allylcysteine, an amino acid derived from garlicView study →Reference 212013Therapeutic uses and pharmacological properties of garlic, shallot and their biologically active compoundsView study →}. Its interaction profile is milder than fresh garlic’s, too: the antiplatelet/anticoagulant caution attached to garlic comes chiefly from allicin, ajoene and the diallyl sulfides, and SAC itself is only a weak antiplatelet agent, so the isolate carries less bleeding risk. The standard garlic caution with warfarin, antiplatelets and around surgery still applies when it is taken as AGE (a whole extract) ^{21Reference 212013Therapeutic uses and pharmacological properties of garlic, shallot and their biologically active compoundsView study →}.

Dosage

There is no isolated-SAC human dose, and nothing here is a recommendation. Cardiovascular trials use aged garlic extract at roughly 600–1200 mg AGE/day, with a blood-pressure meta-analysis finding significant benefit only above ~1200 mg/day ^{17,16Reference 17Saadh MJ et al. · 2024Meta-analysisEffects of aged garlic extract on blood pressure in hypertensive patients: a systematic review and meta-analysisView study →Reference 16Ried K et al. · 2016Garlic lowers blood pressure in hypertensive individuals, regulates serum cholesterol and stimulates immunityView study →}; AGE products are standardised to a stated SAC content rather than dosed as free SAC, so these regimens deliver only milligram quantities of SAC embedded in a whole extract.

References