Merck Manual

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Laura Shane-McWhorter

, PharmD, University of Utah College of Pharmacy

Last full review/revision Jul 2020| Content last modified Jul 2020
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Echinacea, a North American wildflower, contains a variety of biologically active substances.


Echinacea is said to stimulate the immune system. When taken at the start of a cold, it is said to shorten the duration of cold symptoms. Well-designed studies have not supported this effect.

Topical preparations are used to promote wound healing.


Studies of echinacea's role in preventing and/or treating the common cold are inconsistent. The largest factor contributing to inconsistency is the variability of plant preparations (including different plant parts and species) and ultimately composition of the supplement.

A 2014 Cochrane review of 24 studies (4631 participants) evaluated a variety of different echinacea products to prevent or treat colds. No benefit was shown for prevention, although a post hoc pooling of prevention studies implied a 10 to 20% relative risk reduction. The authors concluded some products had weak benefit (1). A 2019 systematic review and meta-analysis of randomized trials assessed the impact of echinacea on prevention, duration, and safety for upper respiratory tract infections. There was a significant effect on prevention but no impact on symptom duration and no safety risk (2). However, a limitation was heterogeneity of included studies.

Adverse effects

Most adverse effects are mild and transitory; they include dizziness, fatigue, headache, and gastrointestinal symptoms. No other adverse effects are known. Theoretically, echinacea is contraindicated in patients with autoimmune disorders, multiple sclerosis, AIDS, tuberculosis, and organ transplants because it may stimulate T cells. Allergic reactions are possible in patients with allergies to ragweed, chrysanthemum, marigold, daisies, or related allergens.

Drug interactions

Echinacea inhibits some cytochrome P-450 enzymes and stimulates others; it can therefore potentially interact with drugs metabolized by the same enzymes (eg, anabolic steroids, azole antifungals, methotrexate, etoposide, and other chemotherapeutic drugs).

Echinacea reference

  • Karsch-Volk M, Barrett B, Kiefer D, et al: Echinacea for preventing and treating the common cold. Cochrane Database Syst Rev (2) CD000530, 2014. doi: 10.1002/14651858.CD000530.pub3.

  • David S, Cunningham R: Echinacea for the prevention and treatment of upper respiratory tract infections: a systematic review and meta-analysis. Complement Ther Med 44:18-26, 2019. doi: 10.1016/j.ctim.2019.03.011.

More Information

The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

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