The testosterone gel used in a series of trials assessing health effects. (credit: AbbVie) In decades of research, scientists have found only one medical condition that’s clearly and effectively treated with testosterone supplements: pathological hypogonadism—that’s low testosterone levels due to disease of the hypothalamus, pituitary gland, or testes. But that hasn’t stopped drug makers and the supplement industry from convincing men that jacking their testosterone will stave off the effects of aging.