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Moderate evidenceImmunity

American Ginseng

One of the few cold-prevention supplements with real randomized trials behind it. The positive results all come from a single proprietary extract and largely from industry-linked studies, and an independent trial in patients found nothing.

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What the science says

  • Fewer colds over a season Moderate evidence

    A systematic review of five randomized trials of North American ginseng preparations in healthy adults found reductions in the mean number of colds per person and in symptom duration. The reviewers noted that all trials used the same proprietary extract and that methodological and funding limitations weaken the conclusion.

  • Reduced recurrent respiratory symptoms in a placebo-controlled trial Moderate evidence

    A randomized, double-blind, placebo-controlled trial in community-dwelling adults reported fewer recurrent colds and fewer total symptom days over four months of daily supplementation.

  • No benefit in an independent patient trial Limited evidence

    A randomized controlled trial of the same extract in patients with chronic lymphocytic leukemia did not show a significant reduction in respiratory infections. This is an important counterweight to the healthy-adult results.

Dosage & safety

Studied dose200–400 mg per day of a standardised polysaccharide-rich American ginseng extract, taken through the cold season. Trials ran for two to four months.
SafetyGenerally well tolerated; headache, insomnia and gastrointestinal upset are reported. It can lower blood glucose, which matters if you take diabetes medication, and it has been reported to reduce the effect of warfarin. Avoid alongside immunosuppressant therapy and in pregnancy without medical advice.

How to take it

TimingMorning, because insomnia is one of the more common complaints.
With food?Either way; with food if it upsets your stomach.
Worth knowingThis is a season-long course, not a rescue remedy — the trials dosed it daily for two to four months to reduce how often people got colds.

Interactions

With medications

  • warfarin

    A randomised trial in healthy volunteers found American ginseng reduced warfarin's anticoagulant effect and lowered INR. do not combine without telling the clinic managing your INR

  • insulin, sulfonylureas and other diabetes medication

    American ginseng lowers blood glucose, which adds to the drug's effect. monitor your glucose more closely and discuss the dose with your doctor

  • immunosuppressants such as ciclosporin or tacrolimus

    It is marketed as an immune stimulant and may work against the therapy. avoid it while on immunosuppressive treatment

With other supplements

  • berberine, cinnamon and other glucose-lowering supplements

    Additive blood sugar lowering. do not stack them if you also take diabetes medication

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

Frequently asked questions

Does American ginseng prevent colds?

American ginseng has moderate evidence for reducing colds: randomized trials in healthy adults found fewer colds and shorter symptoms over a season. All positive trials used the same proprietary extract, often with industry links, and an independent trial in leukemia patients found no reduction in infections.

How much American ginseng should I take per day?

Trials used 200–400 mg per day of a standardised polysaccharide-rich American ginseng extract, taken daily for two to four months through the cold season. It is a season-long course, not a rescue remedy.

Can I take American ginseng with warfarin?

Not without telling your INR clinic: a randomised trial found American ginseng reduced warfarin's anticoagulant effect and lowered INR. American ginseng also lowers blood glucose, so monitor closely if you take diabetes medication.

What are the side effects of American ginseng?

American ginseng is generally well tolerated, but headache, insomnia and stomach upset are reported, so take it in the morning. Avoid it alongside immunosuppressant therapy and in pregnancy without medical advice.

Scientific references

Related in Immunity

Herbal medicines: what the evidence says (335)