Metformin, testosterone, or both in men with obesity and low testosterone: A double-blind, parallel-group, randomized controlled trial

Men with obesity tend to be insulin resistant and often have low-normal testosterone concentrations. We conducted a clinical trial aimed to evaluate potential therapeutic strategies for low testosterone in men with obesity. We did a 1-year, parallel, randomized, double-blind, placebo-controlled trial, where we evaluated the independent and combined effects of metformin and testosterone in 106 men with obesity, aged 18–50 years, who had low levels of testosterone and no diabetes mellitus. The primary outcome was change in insulin resistance, measured as Homeostasis Model Assessment for Insulin Resistance (HOMA-IR) index. Secondary outcomes included changes in total and free serum testosterone, body composition, metabolic variables, erectile function, and health-related quality of life (HRQoL). In the intention-to-treat analysis, the HOMA-IR index decreased significantly in all active groups compared to placebo (metformin −2.4, 95 % CI −4.1 to −0.8, p = 0.004; testosterone −2.7, 95 % CI −4.3 to −1.1, p = 0.001; combination −3.4, 95 % CI −5.0 to −1.8, p