What your weight loss drug might be doing to your testosterone

New research on GLP-1s suggests the body's systems are more connected than the prescription suggests.

Most people starting a GLP-1 don't expect it to do anything to their hormones. They expect it to do something to the scale.

The new research suggests something else is happening underneath. The drugs people are prescribed to lose weight may also be doing measurable work on the hormones that govern energy, libido, recovery, and muscle. That second effect was not the goal of the prescription. But it's showing up anyway.

Picture someone six months into a GLP-1 protocol. Twenty pounds down. Clothes fit differently. Sleeping better. They chalk all of it up to the weight loss. They might be missing half the story.

The study

Researchers at SSM Health Saint Louis University Hospital followed 110 adult men with obesity or type 2 diabetes for 18 months while they took GLP-1 medications including semaglutide, dulaglutide, and tirzepatide. The average age was 54. None were on testosterone therapy at baseline. The team measured total and free testosterone before treatment and throughout the protocol. Preliminary findings were presented at ENDO 2025, the Endocrine Society's annual meeting in San Francisco.

The headline number: the proportion of men with normal levels of both total and free testosterone rose from 53% to 77% over the course of treatment. Free testosterone is what your body can actually use, not just what's circulating. Both moved. In the words of lead author Dr. Shellsea Portillo Canales, this is "among the first to provide compelling evidence that low testosterone can be reversed with the use of commonly prescribed anti-obesity medications."

Why it makes sense

Low testosterone is common in men with obesity. Body fat converts testosterone into estrogen via the aromatase enzyme, which signals the brain to slow down its own hormone production. Chronic inflammation interferes with that signaling further. Insulin resistance disrupts the cascade. Until this study, the question was whether treating the metabolic problem with a medication could reverse the hormonal one. The early answer appears to be yes.

The mechanism is still being studied. Weight loss itself raises testosterone in men with obesity, so the GLP-1s may simply be doing their main job and producing a downstream hormonal benefit. There may also be more direct pathways involving insulin sensitivity, inflammation, and the broader metabolic environment. The study only enrolled men, and didn't isolate which factor matters most.

What it did do is point at something worth paying attention to: in people with metabolic dysfunction, the systems we tend to treat separately are not actually separate. Testosterone, body composition, glucose regulation, sleep, recovery. Move one, and the others move with it.

What to do with this information

If you're starting a GLP-1, the right question isn't just "am I losing weight." It's "what else is changing." Testosterone is one obvious marker. Inflammation, lipid profile, fasting insulin, and HbA1c are others. Comprehensive bloodwork, run at baseline and tracked over time, is the only way to know whether your hormones, metabolic numbers, and inflammation markers are moving in the directions they should be.

Most comprehensive protocols run quarterly bloodwork in the first year, then twice yearly once the numbers stabilize. That cadence catches the inflection points without overdoing it. Six months in, you should know whether the medication is doing what you wanted, and whether anything else is moving in a direction worth a conversation.

The medication is a tool. The labs are how you know what the tool is doing.

A weight loss medication without that visibility is a guess. A weight loss medication with that visibility is a protocol.

That distinction is the entire point of a clinical team.

Preliminary findings presented at ENDO 2025 and have not yet undergone peer review.

References

1. Endocrine Society. (2025, July 14). Anti-obesity medications can normalize testosterone levels in men [Press release]. https://www.endocrine.org/news-and-advocacy/news-room/endo-annual-meeting/endo-2025-press-releases/portillo-canales-press-release

2. Mammoser, G. (2025). GLP-1 drugs may improve low testosterone. Healthline. https://www.healthline.com/health-news/glp-1-drugs-may-improve-low-testosterone

3. Burnett-Bowie, S.A.M., et al. (2020). Aromatase Inhibitors Plus Weight Loss Improves the Hormonal Profile of Obese Hypogonadal Men Without Causing Major Side Effects. Frontiers in Endocrinology, 11, 277. https://www.frontiersin.org/journals/endocrinology/articles/10.3389/fendo.2020.00277/full

4. Altered Expression of Aromatase and Estrogen Receptors in Adipose Tissue From Men With Obesity or Type 2 Diabetes. (2025). The Journal of Clinical Endocrinology & Metabolism, 110(10), e3410-e3422. https://academic.oup.com/jcem/article/110/10/e3410/7964961

This blog post is intended for informational purposes only and should not be considered medical advice. Always consult a healthcare professional before making changes to your health routine.