Effect of Testosterone Supplementation With and Without a Dual 5α-Reductase Inhibitor on Fat-Free Mass in Men with Suppressed Testosterone Production: A Randomized Controlled Trial

In a randomized controlled trial published in 2012, researchers investigated the effects of testosterone supplementation with and without the dual 5α-reductase inhibitor dutasteride on fat-free mass and other androgen-dependent processes in men with suppressed testosterone production. The study involved 139 men aged 18 to 50 years, of whom 102 completed the 20-week intervention. Participants were divided into eight groups receiving varying doses of testosterone enanthate (50, 125, 300, or 600 mg/week) with either placebo or 2.5 mg/day of dutasteride. The primary outcome was the change in fat-free mass, with secondary outcomes including changes in fat mass, muscle strength, sexual function, prostate volume, sebum production, and hematocrit and lipid levels. The results showed that the increase in fat-free mass in response to graded doses of testosterone did not significantly differ between the dutasteride and placebo groups, suggesting that the conversion of testosterone to dihydrotestosterone (DHT) is not essential for testosterone's anabolic effects on muscle. Changes in other measured outcomes also did not differ significantly between the groups.