What a GLP-1 Does to Him

The short version

Plenty of households now have two prescriptions in the refrigerator, and almost everything written for women about these drugs stops at her body. This page is about his — testosterone, sperm, erections — because those are the questions that actually get asked once the second box arrives, and because the answers turn out to matter to a decision the two of you might be making together.

What happens between you is a different subject, covered in what a GLP-1 does to a marriage; your own desire is covered in desire on a GLP-1. Neither of those touches the physiology below.

The headline: the evidence is early, it is mostly in men who were already unwell, and it contains one genuinely surprising result that cuts against the obvious treatment.

Testosterone goes up, and the reason is unglamorous

Obesity lowers testosterone through a well-described route — fat tissue converts testosterone to estradiol, which suppresses the signal from the brain that tells the testes to make more. The clinical name for the result is functional hypogonadism, meaning the machinery works but the instructions have been turned down. Lose the weight and the signal usually recovers.

That is the mechanism doing most of the work in the GLP-1 data, and it is worth saying plainly, because it is not a drug effect on the testes so much as a weight effect arriving by a new route. A controlled pilot study enrolled 83 men with obesity and metabolic hypogonadism, put everyone on a reduced-calorie diet and twenty minutes of daily walking, and then split them three ways: tirzepatide, no drug, or transdermal testosterone, with hormone panels and an erectile-function questionnaire at two months¹. Its authors position tirzepatide as promising specifically for hypogonadism that arose from metabolic causes — which is the population, not a general claim about men.

Sperm: one small trial, and the result that should change a decision

This is the part worth reading twice.

A randomized open-label trial gave 25 men with type 2 diabetes and functional hypogonadism either semaglutide 1 mg weekly or intramuscular testosterone undecanoate, for 24 weeks, with semen analysis before and after². Everyone started with poor sperm quality — below the fifth percentile of reference values.

Read the last two rows together, because they are the point. Both treatments raised testosterone, and participants in both arms reported fewer hypogonadism symptoms on the AMS questionnaire. But erectile scores improved only on testosterone — while testosterone was simultaneously driving sperm concentration and count down. Semaglutide did the reverse.

That is not a footnote. Testosterone therapy is the obvious prescription for a man with low testosterone, and it is contraceptive in effect: supplementing from outside tells the brain to stop signaling, and sperm production falls with it. If the two of you are trying to conceive, the obvious treatment and the desired outcome point in opposite directions, and this trial is a small, direct demonstration of that.

Hold it loosely all the same. Twenty-five men, open-label, 24 weeks, everyone diabetic and hypogonadal to begin with. A 2% to 4% shift in normal forms is real and statistically significant and still leaves the sample far below normal reference values. A narrative review of this literature reaches the same cautious place — GLP-1 receptor agonists show promise for sperm parameters in men with obesity, and clinical trials with longer follow-up are needed before anyone knows what it means³.

Erections: the evidence genuinely points both ways

You would expect improvement. Erectile function is largely vascular, these drugs improve vascular health, and weight loss on its own tends to help.

Mostly the literature agrees — but not unanimously. A 2025 narrative review set out to synthesize exactly this question and found that while experimental and clinical work supports a positive effect, preliminary reports have also raised concerns about a possible association between GLP-1 use and erectile dysfunction⁴. Its title asks whether these drugs are friend or foe, which is a fair summary of where the field sits. The trial above is consistent with that ambiguity: semaglutide produced no significant change in erectile scores over six months.

So the honest answer to "will it help him in bed" is that it may, that a minority report the opposite, and that nobody has run the study that would settle it.

If you are trying to conceive

Three things follow, and only three.

A GLP-1 is not a fertility treatment. The sperm result is one small trial in men who were unwell, and the review behind it asks for confirmation rather than offering a recommendation.

Testosterone therapy and trying to conceive are in tension. That is not a GLP-1 finding — it is long-established andrology — but this trial puts the two side by side in the same men, and it is the single most actionable thing on this page. It belongs in a conversation with whoever is prescribing.

Your own washout is a separate question with its own timing, covered on trying to conceive on a GLP-1. Nothing here changes it.

Where this sits on the evidence scale

Testosterone rises as weight falls: strong, and long-established. The mechanism predates these drugs; the GLP-1 data are consistent with it rather than proving something new.

Semaglutide improves sperm morphology: low. One randomized open-label trial, 25 men, all with diabetes and hypogonadism, 24 weeks. Directionally interesting; nowhere near a recommendation.

Testosterone therapy suppresses sperm: strong. Well-established andrology, and reproduced here as a secondary finding.

Effect on erections: contested. A 2025 review finds supportive evidence and preliminary reports pointing the other way, and calls for research. Treat any confident claim in either direction as marketing.