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Limited evidenceImmunity

Allicin (Stabilized)

The sulphur compound formed when garlic is crushed, and a potent antimicrobial in a test tube. In humans the entire cold-prevention case rests on one trial from 2001 that has never been repeated.

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What the science says

  • One trial, never replicated Limited evidence

    A Cochrane review of garlic for the common cold identified only a single randomized trial meeting inclusion criteria. The reviewers concluded that there is insufficient evidence to recommend garlic for preventing or treating colds, and that more trials are needed.

  • The original trial reported fewer colds Limited evidence

    That trial gave an allicin-containing garlic supplement or placebo to volunteers over twelve winter weeks and recorded markedly fewer colds in the treated group. Colds were self-reported in a diary, the reporting of methods was incomplete, and no independent group has reproduced it.

  • Antimicrobial activity does not transfer to the body Limited evidence

    Allicin kills bacteria, fungi and viruses in culture at concentrations that are not achievable in blood after swallowing a supplement. It is also chemically unstable, which is why products advertise an allicin yield rather than an allicin content.

Dosage & safety

Studied doseThe single positive trial used a garlic powder supplement providing about 180 mg of allicin-releasing powder daily. Commercial products state an allicin yield, commonly 2–12 mg per day.
SafetyGarlic breath and body odour, heartburn and gastrointestinal upset are common. Garlic inhibits platelet aggregation, so caution with anticoagulants and stop before surgery. It can lower blood levels of saquinavir and possibly other drugs. Avoid high-dose supplements in pregnancy.

How to take it

TimingTiming does not matter.
With food?With food, which markedly reduces the heartburn and stomach upset.
Worth knowingRead the allicin yield rather than the powder weight, and choose an enteric-coated tablet if breath odour is the reason you would otherwise stop.

Interactions

With medications

  • warfarin, aspirin, clopidogrel and other anticoagulant or antiplatelet drugs

    Garlic inhibits platelet aggregation, adding to bleeding risk. do not use high-dose supplements on these drugs, and stop at least a week before surgery

  • saquinavir and other HIV protease inhibitors

    Garlic supplements lower blood levels of saquinavir, risking loss of viral control. do not combine without your HIV team's agreement

With other supplements

  • fish oil, ginkgo, vitamin E and other bleeding-risk supplements

    Additive effect on clotting. avoid stacking them around surgery or dental work

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Does allicin or garlic prevent colds?

The evidence is limited: the case for allicin in cold prevention rests on one 2001 trial with self-reported colds that has never been replicated. A Cochrane review found insufficient evidence to recommend garlic for preventing or treating colds.

Does allicin kill bacteria and viruses in the body?

Allicin kills bacteria, fungi and viruses in a test tube, but only at concentrations that cannot be reached in the blood after swallowing a supplement. Allicin is also chemically unstable, which is why labels state an allicin yield.

How much allicin per day?

The single positive trial used about 180 mg of allicin-releasing garlic powder daily. Commercial allicin products state an allicin yield, commonly 2–12 mg per day; taking it with food reduces heartburn.

Is allicin safe with blood thinners?

Garlic inhibits platelet aggregation, so do not use high-dose allicin supplements on warfarin, aspirin, clopidogrel or similar drugs, and stop at least a week before surgery. Allicin supplements also lower saquinavir levels, so avoid them on HIV protease inhibitors without your HIV team's agreement.

Scientific references

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