Pilot study reports tirzepatide raises testosterone and improves erectile function in men with obesity

A pilot study published July 2, 2025, in Reproductive Biology and Endocrinology found that tirzepatide, the active ingredient in Zepbound and Mounjaro, raised testosterone levels and improved erectile function in men with obesity and low testosterone more than either lifestyle changes alone or testosterone replacement therapy.^[1] The findings were also presented at the ENDO 2025 meeting in San Francisco.^[2]

Researchers at the University of Catania in Italy enrolled 83 men with obesity and what is called metabolic hypogonadism, a condition in which excess body fat disrupts normal testosterone production.^[1] To qualify, men needed a body mass index of 30 to 39.9, a waist circumference over 94 centimeters, severe erectile dysfunction that had not improved with prior treatment, low total testosterone, and other hormone markers consistent with obesity-related hypogonadism.^[2]

Patients chose, rather than were randomly assigned to, one of three groups: 28 men took tirzepatide, starting at 2.5 mg weekly for one month before increasing to 5 mg, along with diet and daily walking; 30 men followed the diet and walking plan alone; and 25 men used transdermal testosterone every other day plus the same lifestyle plan.^[1][2] Average ages ranged from about 54 to 56 across groups, and there were some baseline differences, including higher waist circumference in the lifestyle-only group and higher lean mass and luteinizing hormone in the tirzepatide group.^[1]

After two months, the tirzepatide group had significantly greater drops in body weight, waist circumference, and fat mass, along with more lean mass gain, than the other two groups.^[1] Tirzepatide also produced significantly higher increases in luteinizing hormone, follicle-stimulating hormone, sex hormone-binding globulin, total testosterone, free testosterone, and bioavailable testosterone compared with both other groups, while estradiol levels were lower.^[1] Erectile function scores, measured with the IIEF-5 questionnaire, improved more with tirzepatide than with lifestyle change alone, and the improvement was similar to that seen with testosterone therapy.^[2]

Study author Rossella Cannarella, an endocrinologist at the University of Catania, said the reversal of hypogonadism in all tirzepatide-treated patients was "really a remarkable finding."^[2] She noted that because tirzepatide raised gonadotropin levels rather than suppressing them, as testosterone therapy can, it might be a useful option for men who want to preserve fertility, though she said this needs to be confirmed by testing sperm parameters directly.^[2]

Why it matters for patients

Men with obesity who also have low testosterone and erectile dysfunction sometimes face a choice between weight-loss strategies and hormone therapy, which can suppress the body's own testosterone production and affect fertility.^[1][2] This small study suggests tirzepatide might address both weight and hormone levels at once, without the fertility trade-offs associated with testosterone replacement.^[2] However, the study allocated patients by their own preference rather than by random assignment, which means the groups may have differed in ways researchers could not measure, and the results could reflect factors other than the drug itself.^[1] The study also lasted only two months, so it does not show whether these effects persist over time.^[1]

What happens next

The researchers say more work is needed to look at how tirzepatide affects sperm quality directly, since this pilot only measured hormone levels rather than sperm parameters.^[2] Larger, randomized trials with longer follow-up would be needed to confirm these results and determine whether the hormone and erectile-function improvements are durable.^[1]