Testosterone builds muscle but has risks

Like most performance-enhancing drugs, testosterone can help athletes build bigger, stronger muscles very quickly, improving their athletic ability and their recovery time - but testosterone carries significant health risks that aren't fully understood yet.

It's unclear whether Giants outfielder Melky Cabrera was using natural testosterone or a synthetic version of the hormone, but both kinds are a form of anabolic steroid.

The body produces testosterone to promote growth in men and women and to regulate masculine characteristics, such as a deep voice and the development of sex organs in men.

It's muscle growth and quick recovery that athletes who abuse steroids are after. Testosterone - whether it's injected, applied via a patch or cream, or taken by pill - allows athletes to rapidly increase muscle mass beyond what their body would generally manage, and also reduces their recovery time, meaning they can train hour after hour, day after day, with little need to rest their bodies in between workouts.

"Testosterone can help increase muscle mass in a much faster fashion. Athletes who use anabolic steroids may find that they're able to increase their endurance and their strength by doing the same amount of training as they would otherwise," said Dr. Anthony Yin, an endocrinologist at California Pacific Medical Center in San Francisco.

Major League Baseball has banned testosterone use by its ballplayers, but Yin noted that the hormone is an important and federally approved medical treatment.

Men who are testosterone-deficient can get hormone replacement therapy, and the hormone also is given to children with developmental or growth problems. Doctors sometimes give testosterone to patients with muscle-wasting diseases like cancer or AIDS.

But the side effects can be brutal, especially because testosterone must be given regularly over a long period to be effective. Side effects include liver damage, unsafe cholesterol levels, and heart and circulatory problems. Testosterone abuse may affect the prostate and cause cancer, as well.

Men who chronically abuse testosterone may experience effects that would seem to be contrary to the hormone's purpose, including breast development, shrunken testicles, and infertility.

And the side effects may not end there. Most of the known risks associated with testosterone use come from clinical trials applying the hormone for medical treatment, or from anecdotal evidence among athletes.

It would be unethical for researchers to attempt a scientific study of steroid abuse in athletes, which means the full range of side effects is unknown.

"Testosterone use can lead to several undesirable effects, whether it's used for therapeutic purposes or in situations such as this," Yin said. "There are certainly potential benefits if you can call them that. But testosterone has those negative points too."

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Testosterone builds muscle but has risks

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