Back in the late ’90s, the term “prohormone” took on a negative connotation when baseball player Mark McGwire revealed that he was using androstenedione, a prohormone supplement, while he was suspected of using steroids. McGwire did ultimately admit to juicing, and perhaps as a result, prohormones fell into disfavor, forever (wrongly) associated with illegal steroid use.

But prohormones are supplemental and naturally occurring substances that provide the raw materials or precursors the body needs to make crucial hormones. Many of them are necessary for health, and some are also beneficial for supporting muscle growth and secondary sex characteristics. Many legal products today contain prohormones that help boost testosterone, growth hormone and insulin-like growth factor-1, among others. When your goal is to boost muscle mass through supplementation of legal prohormones, just make sure that they’re allowed by the athletic associations you compete within, and follow labeling directions for best results. <