Allium sativum · food
Evidence tier: moderate
A foundational kitchen herb with serious cardiovascular and antimicrobial credentials. Aged garlic extract is gentler than raw for daily use.
Allicin, generated when alliin meets the enzyme alliinase on crushing, is the source of garlic's antimicrobial activity and most of its smell; it is unstable, which is why preparations differ so much. The blood pressure mechanism is thought to run through hydrogen sulfide and nitric oxide signalling causing vasodilation and lower peripheral resistance. The antiplatelet effect, and therefore the bleeding risk, is a direct consequence of the same organosulfur chemistry. The saquinavir interaction runs through induction of cytochrome P450 and intestinal first pass metabolism, meaning garlic can accelerate the clearance of other drugs handled by that system.
Moderate for blood pressure, weak to negative for cholesterol, and the two must not be sold as one claim. On BLOOD PRESSURE the evidence is modest but real: NCCIH concludes that garlic supplements may reduce blood pressure to a small extent IN PEOPLE WHO HAVE HIGH BLOOD PRESSURE, and meta analytic work (Ried) puts the reduction in hypertensive subjects at roughly 8 mmHg systolic and 5 mmHg diastolic. Note the qualifier carefully, because it is the whole ballgame: the effect appears in people who already have hypertension, which is a diagnosed disease population, not in normotensive consumers. On CHOLESTEROL the better the trial, the worse garlic performs. The most rigorous test ever run, Gardner's 2007 Stanford RCT (Archives of Internal Medicine, 192 adults with LDL of 130 to 190 mg/dL, six months, four arms) tested raw garlic, powdered garlic and aged garlic extract against placebo and found that NONE of the three lowered LDL. NCCIH still describes a small reduction in total and LDL cholesterol across the pooled literature, but the pooled literature is dominated by shorter and weaker trials, and the single best trial is flatly negative. Cancer prevention is negative or uncertain: NCCIH says consuming garlic does not seem to reduce stomach cancer risk and that its effect on colorectal cancer risk is uncertain. Immune and common cold support, which the seed asserts, has almost no evidence: NCCIH notes a 2022 review found only TWO small studies. The safety half of the file is where garlic actually earns attention. Garlic increases bleeding risk (NCCIH advises telling your provider, and the effect matters before surgery), and garlic is a potent CYP inducer: an NIH pharmacokinetic study found garlic supplements cut the blood levels of the HIV protease inhibitor saquinavir roughly in half (AUC down 51 percent, Cmax down 54 percent, trough down 49 percent), a real and clinically serious interaction that persists partway through a 10 day washout.
600 to 1,200 mg of aged garlic extract daily is the range used in the blood pressure trials, or 1 to 2 fresh cloves crushed and eaten with food. Preparations are not interchangeable: raw, powdered and aged garlic differ in allicin yield, and Gardner tested all three against LDL and none worked.
600 to 1200 mg aged garlic extract daily, or 1 to 2 fresh cloves crushed and eaten with food.
Significant anticoagulant interaction, avoid before surgery. May cause GI upset and breath odour.
Pregnancy: caution
Breastfeeding: caution
Active compounds: allicin, alliin, S-allyl cysteine, diallyl disulfide, ajoene
Remedies using Garlic · Browse by body system · Check it against what you take
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.