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.
Most adverse effects are mild and transitory; they include dizziness, fatigue, headache, and GI symptoms. No other adverse effects are known. Theoretically, echinacea is contraindicated in patients with autoimmune disorders, multiple sclerosis, AIDS, TB, and organ transplants because it may stimulate T cells. 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). Allergic reactions are possible in patients with pollen allergies.
Last full review/revision May 2009 by Ara DerMarderosian, PhD