Be aware that herbal supplements sometimes include anabolic steriods, ephedrine, caffeine, and other substances that may not be listed on the label and may cause you to fail a drug test in your sport. More important, they may damage your health.

Some early research has claimed that ginseng supplements can improve exercise performance, but that research has many flaws. More recent, better-controlled experiments have failed to show any positive effect of either Chinese or Siberian ginseng on performance.

So-called "muscle building" anabolic herbs, including yohimbine, smilax, tribulus, wind yams and gamma oryzanol are unlikely to have any effect on your muscles. The plant steriods found in many of these herbs cannot be converted by the human body into testerone or other anabolic steriods. Claims that there agents can increase muscle mass have little or no scientific basis.

Yohimbine can raise blood pressure, cause nerve paralysis, stomach and kidney disorders, seizures, and even death. Smilax stimulates urination, bowel evacuation, sweating, and coughing, any of which could be harmful to sport performance. Tribulus and oryzanol are probably safe when used at recommended dosages.

The active ingredients in the ephedra herb ephedrine, which is banned by sport governing bodies and can be very dangerous, leading to strokes and death. Although synthetic ephedrine combined with caffeine may improve exercise performance somewhat, the herbal products, i.e., ephedra, seems to be ineffective, perhaps because of variation in the potency of ephedrine contained in the herbal extracts.

Ephedra stimulates the nervous system in much the same way as caffeine, so it can make an athlete feel energized, but it does not supply energy.

Herbs can be especially dangerous when taken with certain prescription drugs or over-the-counter medications. You should tell your physician about any herbal supplements you are taking.

Don't expect herbal supplements to take the place of hard training as a means of improving performance.