Effect of Testosterone Supplementation With and Without a Dual 5α-Reductase Inhibitor on Fat-Free Mass in Men With Suppressed Testosterone Production

The study, conducted on 139 men aged 18 to 50 years, with 102 completing the intervention, aimed to assess the necessity of dihydrotestosterone (DHT) in testosterone's anabolic effects on muscle by comparing testosterone supplementation with and without the 5α-reductase inhibitor dutasteride. The primary outcome was the change in fat-free mass, and secondary outcomes included muscle strength and various health markers. The study found no significant difference in the increase of fat-free mass or any secondary outcomes between the groups receiving testosterone with dutasteride and those receiving testosterone with a placebo. This suggests that the conversion of testosterone to DHT is not essential for testosterone's anabolic effects on muscle. The study had sufficient power to detect a 25% difference in outcomes, providing strong evidence for the conclusion.