Evaluation of echinacea for treatment of the common cold.

Considered to have immunostimulating activity, echinacea is a widely used phytomedicinal for treatment of the common cold and upper respiratory tract infections (URTIs). We reviewed the literature from the MEDLINE database (January 1966-July 1999), International Pharmaceutical Abstracts (IPA) online database, Cambridge Scientific Abstracts Biological Sciences online database, Alt-Health Watch online database, EMBase CD-ROM database, and references from published articles, reviews, and letters to evaluate evidence from clinical trials of echinacea's purported efficacy for treating or preventing URTIs. Twelve clinical studies published from 1961-1997 concluded that echinacea was efficacious for treating the common cold, but the results are unclear due to inherent flaws in study design. Five trials were published since 1997; two showed that echinacea lacked efficacy for treating and preventing URTI symptoms, and three concluded that it was effective in reducing the frequency, duration, and severity of common cold symptoms. Again, these results are unclear because of methodologic uncertainties, such as small populations and use of noncommercially available, nonstandardized dosage forms. Although evidence for echinacea's efficacy is inconclusive, it appears to be safe. Patients without contraindications to it may not be dissuaded from using an appropriate preparation to treat the common cold.