From CNN Medical Correspondent Dr. Steve Salvatore

NEW YORK (CNN) -- Slugger Mark McGwire's controversial use of androstenedione has spurred Major League Baseball and the players union to look into dietary supplement use in players.

Both organizations have asked a medical team to gather all available information about the drug and other supplements.

McGwire and many other athletes take androstenedione to increase the testosterone levels in their body with the notion that building bigger muscles will enhance their performance.

"We don't know if this drug does increase testosterone levels," said Dr. Charles Yesalis, author of the "The Steroids Game." "The current state of the art on this drug is that we don't even know if it works as a performance enhancer."

Androstenedione is a hormone produced in men and women. In men, it's produced by the adrenal glands and the testes. In the body, it is readily converted to testosterone, the most potent male sex hormone.

Androstendione will help build bigger muscles

"The question is, is it an anabolic steroid -- does it build muscle mass and strength?" Yesalis said. "The answer to that is, we simply don't know."

Experts do agree androstenedione would probably have to be given into a vein or by injection into muscle to have an effect. Athletes tend to take the supplement in pill form, which experts say would be less likely to work.

In spite of the small amount of real scientific research supporting supplements like androstenedione, body builders swear by them. But experts say they may be experiencing a placebo effect.

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"What happens is you get on theses pills and then you get on a regiment that's much stricter than the regimen you might otherwise have gotten on had you not been taking the pills, and it becomes a self-fulfilling prophecy," said Dr. William Rosner of St. Lukes-Roosevelt Hospital in New York.

Doctors warn androstenedione is distributed as a natural substance and is not regulated by the U.S. Food and Drug Administration.

Recently, health food stores have seen a surge in sales. Doctors fear these supplements are getting into the hands of teenagers.

"Not only don't we know whether this drug works or not, but we don't know if its health effects are either short-term or long-term," Yesalis said. "Consequently you're rolling the dice and taking a chance."