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.

Evidence last reviewed: August 2026

View on iHerb Ships to 180+ countries · welcome discount for new customers

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.

Scientific references

North American (Panax quinquefolius) and Asian Ginseng (Panax ginseng) Preparations for Prevention of the Common Cold in Healthy Adults: A Systematic Review
Seida JK, Durec T, Kuhle S — Evid Based Complement Alternat Med, 2011
Efficacy of COLD-fX in the prevention of respiratory symptoms in community-dwelling adults: a randomized, double-blinded, placebo controlled trial
McElhaney JE, Goel V, Toane B, Hooten J, Shan JJ — J Altern Complement Med, 2006
A randomized, controlled trial of Panax quinquefolius extract (CVT-E002) to reduce respiratory infection in patients with chronic lymphocytic leukemia
High KP, Case D, Hurd D, Powell B, Lesser G, Falsey AR, Siegel R, Metzner-Sadurski J, Krauss JC, Chinnasami B, Sanders G, Rousey S, Shaw EG — J Support Oncol, 2012

Where to buy

View on iHerb

Ships to 180+ countries · welcome discount for new customers

Referral link — this site may earn a commission on purchases.

Related in Immunity

Vitamin C Limited evidence
Zinc Moderate evidence
Elderberry Limited evidence
L-Lysine Limited evidence
Echinacea Limited evidence
Andrographis Moderate evidence