One of the more persistent questions surrounding GLP-1 medications has been their effect on testosterone in men. Given that rapid weight loss and caloric restriction can sometimes negatively impact hormone levels, the concern isn't unreasonable. However, the emerging data tells a more nuanced—and largely positive—story.
The 2025 Endocrine Society Study: 110 Men, 18 Months
At the Endocrine Society's ENDO 2025 annual meeting, researchers from SSM Health St. Louis University Hospital presented what they described as "among the first to provide compelling evidence that low testosterone can be reversed with the use of commonly prescribed anti-obesity medications."1
The study analyzed electronic health records of 110 adult men with obesity or type 2 diabetes being treated with semaglutide, dulaglutide, or tirzepatide who were not on testosterone therapy. Participants' hormone levels were tracked over 18 months.
Total testosterone increased from 312 ng/dL at baseline to 368 ng/dL after treatment (P<0.001). Free testosterone also increased from 6.7 ng/dL to 7.2 ng/dL (P=0.04). Participants lost approximately 10% of body weight during the study period.
"Results from this study show that there is a direct correlation between the use of anti-obesity medications and testosterone levels," said lead researcher Dr. Shellsea Portillo Canales. "Doctors and their patients can now consider this class of medications not only for the treatment of obesity and to control blood sugar, but also to benefit men's reproductive health."2
Semaglutide vs. Testosterone Replacement: Head-to-Head
Perhaps the most clinically relevant data comes from a randomized controlled trial conducted at the University Medical Centre Ljubljana, comparing semaglutide directly against testosterone replacement therapy (TRT) in men with type 2 diabetes, obesity, and functional hypogonadism (low testosterone with symptoms).3
Twenty-five men (average age 50, average BMI 35.9 kg/m²) with confirmed low testosterone (below 11 nmol/L) were randomized to either semaglutide 1 mg/week or intramuscular testosterone undecanoate for 24 weeks.
| Outcome | Semaglutide | TRT | P-value |
|---|---|---|---|
| Testosterone increase | Significant ↑ | Significant ↑ | NS (comparable) |
| Hypogonadism symptoms (AMS score) | Improved | Improved | NS (comparable) |
| Erectile function (IIEF-15) | No change | Improved | TRT superior |
| Sperm concentration change | +16.7% | -60.6% | P=0.039 |
| Normal sperm morphology | 2%→4% | No change | Semaglutide superior |
| Weight loss | 115→99 kg (P=0.004) | No change | Semaglutide superior |
The study's conclusion: "Semaglutide was superior to TRT in improving body composition and comparably increased testosterone along with improved [hypogonadism symptom] score." For men wanting to preserve fertility, this finding is particularly important—TRT suppresses natural testosterone production and impairs sperm production, while semaglutide appears to improve sperm quality.4
Why GLP-1s Increase Testosterone
The mechanism behind GLP-1 medications' testosterone-boosting effect appears primarily related to weight loss and metabolic improvement, though direct effects are also possible.
The Obesity-Testosterone Connection
Obesity significantly contributes to male hypogonadism through several mechanisms. More than one-third of men with type 2 diabetes and obesity have functional hypogonadism—low testosterone without any structural cause.5
Excess body fat increases the conversion of testosterone to estrogen in adipose tissue. Insulin resistance, common in obesity and type 2 diabetes, impairs hormonal regulation at the hypothalamic-pituitary-gonadal (HPG) axis. Decreased insulin and leptin signaling disrupt the normal feedback loops that control testosterone production.
By facilitating substantial weight loss and improving insulin sensitivity, GLP-1 medications address these underlying causes rather than simply replacing the missing hormone.
Potential Direct Effects
GLP-1 receptors are distributed along the HPG axis, suggesting potential direct effects on reproductive hormone regulation beyond weight loss alone. Research indicates GLP-1 agonism may have anti-inflammatory effects on reproductive tissues and can directly stimulate metabolic effects on sperm.6
GLP-1 Treatment
Testosterone Replacement
What About Men Without Diabetes?
The data is less clear for men without diabetes or obesity-related hypogonadism. A 2024 study published in the Journal of Sexual Medicine found a slightly increased risk of erectile dysfunction in non-diabetic men prescribed semaglutide for weight loss, though this finding requires confirmation in larger studies.7
Several factors may explain different responses in different populations. Men with naturally low testosterone due to obesity may benefit from weight loss restoring normal levels. Men with already-normal testosterone levels may not see the same benefits. Rapid weight loss and caloric deficits could, in some cases, temporarily affect hormone production regardless of medication used.
Clinical Implications
For men with obesity, type 2 diabetes, and low testosterone, these findings suggest GLP-1 medications may offer a dual benefit—addressing metabolic health while potentially reversing obesity-related hypogonadism. Importantly, unlike testosterone replacement therapy, GLP-1 treatment doesn't suppress natural hormone production or impair fertility.
Some clinicians are now considering combining GLP-1 medications with TRT for select patients. "This seems to be a nice combination for the person who has low testosterone and is trying to lose weight, but just doesn't necessarily have the energy to be able to go and do workouts," notes Dr. Taylor Kohn of Baylor College of Medicine.8
However, this combination is not recommended for men with normal testosterone levels, and certain conditions (history of pancreatitis, medullary thyroid cancer) remain contraindications for GLP-1 therapy regardless of testosterone status.
The Bottom Line for Men
The research to date suggests that concerns about GLP-1 medications lowering testosterone in men with obesity are largely unfounded—the opposite appears to be true. For men with obesity-related low testosterone, GLP-1 therapy may offer a way to address both metabolic health and hormonal balance while preserving fertility options that TRT would eliminate.
That said, individual responses can vary, and men concerned about hormone levels should discuss monitoring with their healthcare provider before and during treatment.