Ginseng

There are three main types of ginseng: Korean/Asian ginseng (Panax ginseng), endangered American ginseng (Panax quinquefolius), and Siberian ginseng (Eleutherococcus senticosus), which is not a "true" ginseng. Products vary, depending on the type of ginseng, how they are processed, and what plant parts are used—leaves, roots, or stems, all of which have different chemical compounds. Ginseng contains active ingredients, called ginsenosides, and many other compounds. It’s not known which are most important, and though the herb has been used for thousands of years, scientists are still largely in the dark about its medicinal effects.

Claims, purported benefits: Treats, cures, or prevents disorders ranging from the common cold to diabetes; improves memory, immunity, sexual performance, and mood; boosts energy and athletic skills.

Evidence: Many human studies have suggested benefits, but nearly all are of poor quality or do not specify what type of ginseng was used or which ginsenosides they contained. A few well-designed studies have not borne out some of the claims—for instance, that ginseng boosts athletic performance or energy. One patented, standardized extract of American ginseng root called Cold-fX has been tested in several small well-designed studies, with promising results. Health Canada (the equivalent of the FDA in the U.S.) has approved Cold-fX, which is now allowed to claim, at least in Canada, that it "helps reduce the frequency, severity, and duration of cold and flu symptoms by boosting the immune system."

Bottom line: There's no convincing evidence to support the use of ginseng, except perhaps for Cold-fX. It’s especially hard to know what you’re getting when you buy ginseng products. Most ginseng is not standardized, and the best grades are expensive. You may pay for ginseng and get very little, if any, or it may be contaminated with other plant substances. It is generally safe, but interactions with blood thinners (such as warfarin) and other drugs are possible; mild side effects include nausea, diarrhea, insomnia, and headaches.