One of the two anabolic steroids for which Alex Rodriguez tested positive, according to published reports, was Primobolan, a drug that is illegal to sell or market in the United States. Terry Todd, a former champion power lifter, said Primobolan had long been a popular drug among athletes. Todd is director of the H. J. Lutcher Stark Center for Physical Culture and Sports at the University of Texas. Todd said that Primobolan was known for building strength without much muscle bulk, and also for having few side effects. He explained that male athletes using Primobolan would not have enlarged breasts, shrunken testicles or a higher voice because the drug, unlike some other steroids, did not convert to estrogen after it was taken.
"It's a drug that you take when you don't want all of the behavior changes that may go along with other steroids," Todd said. "But still, you would also have to feel that you wouldn't be tested, or that there would be no consequences to you getting caught. It's not a miracle pill."
The New York Times
A Steroid Popular for Its Limited Side Effects