A shot of testosterone can really perk up a guy’s day and night, according to Dr. Glenn Wagner of the New York State Psychiatric Hospital. Wagner and colleagues studied the effects of three months of biweekly injections of testosterone in 66 men with HIV with “clinical hypogonadism,” a condition that can cause a decreased interest in sex, as well as depression, general fatigue and a loss in muscle mass. Three quarters of those treated had full-blown AIDS and half had experienced such a drain in overall energy that they had left their jobs and gone on disability.

After 12 weeks on testosterone, 79 percent reported a significant return in energy and a lightening in mood. The jury is still out on whether the mood-lifting effects stemmed from the testosterone itself or from boosted energy levels. Fatigue and depression, the researchers said, is a case of the chicken and the egg.

Some of the side effects experienced included return-to-adolescence acne and testiness (known as “’roid rage” in the weightlifting set) but, as the respondents reported, the benefits of feeling 18 again outweighed the bad.

One caution: Other researchers have warned that long-term testosterone injections may shut down the body’s remaining natural testosterone production and result in impotence. They prefer through-the-skin delivery of the drug using either patches or—least expensive—creams or gels mixed by compounding pharmacists (who create meds to order).