Don't confuse anabolic steroids with corticosteroids, warns physiatrist Kenneth Mautner, MD, of Emory University. Anabolic steroids are used to build up muscle. Corticosteroids are used to dampen overactive immune responses and reduce swelling.

The anabolic steroids abused by athletes are synthetic versions of testosterone, a male hormone. Both men and women naturally produce testosterone. But like all hormones -- which regulate the body's most basic functions -- throwing one's testosterone out of balance can have wide-ranging consequences.

Doctors prescribe anabolic steroids to treat certain specific medical conditions. For example, they may be used to treat the muscle wasting seen in AIDS. Steroids may also be used to treat delayed puberty or loss of testicular function.

Mautner notes that doctors are not allowed to prescribe steroids to enhance a person's athletic performance.

Yes. Without a doctor's prescription for a medical condition, it's against the law to possess, sell, or distribute anabolic steroids.

Legal prosecution can be a serious side effect of illicit steroid use. Under federal law, first-time simple possession of anabolic steroids carries a maximum penalty of one year in prison and a $1,000 fine. For first-offense trafficking in steroids, the maximum penalty is five years in prison and a fine of $250,000. Second offenses double this penalty. In addition to federal penalties, state laws also prohibit illegal anabolic steroid use.

Since steroids are often taken by injections, there is also the risk of getting HIV or hepatitis infection from an unsterile needle or syringe.

"There are a lot of side effects of steroids," Mautner tells WebMD. "They are not good for you. It is like Russian roulette. Five people may take them and have no long-term problem. The sixth may end up dead."