In men carrying excess weight or living with type 2 diabetes, GLP-1 drugs like semaglutide (Ozempic and Wegovy) and tirzepatide (Mounjaro and Zepbound) tend to raise testosterone, may improve fertility markers, and probably help erections. The catch is that almost all of this comes from one thing: weight loss. These medicines are not testosterone treatments or erection pills. They shift the metabolic conditions that were quietly dragging your hormones and blood vessels down in the first place.

Because so many men are now taking these drugs, it is worth understanding what actually happens below the belt. This article walks through the latest clinical evidence from 2024 to 2026 across three areas men ask about most: testosterone, fertility and erections. We will keep the science plain, flag where the research is genuinely uncertain, and be clear about the one safety point that matters if you are planning a family.

How GLP-1 drugs work, and why they reach men's health

GLP-1 stands for glucagon-like peptide-1, a hormone your gut releases after you eat. GLP-1 receptor agonists are medicines that copy this hormone. They tell your brain you are full, slow how fast your stomach empties, and help your body handle blood sugar. The result, for most men, is meaningful weight loss and better blood sugar control.

So why does a weight loss drug touch testosterone, sperm and erections? Because body fat is not a passive store. Fat tissue contains an enzyme called aromatase, which converts testosterone into oestrogen. The more fat a man carries, the more testosterone gets converted away, and the lower his levels tend to run. Excess weight also drives insulin resistance and low-grade inflammation, both of which further blunt the brain signals that tell the testicles to make testosterone.

This is why so many men with obesity develop what doctors call functional or obesity-related hypogonadism (low testosterone caused by the body's condition rather than a fault in the testicles themselves). It is common: research suggests around three quarters of men with severe obesity have low testosterone. The encouraging part is that this type of low testosterone is often reversible. Take away the excess fat and the machinery frequently starts working again.

GLP-1 drugs are simply a powerful new lever for that weight loss. There is early laboratory evidence that GLP-1 receptors also sit directly on the testicles and in the brain's hormone-control centres, hinting at a more direct role. But in humans, the weight loss explanation is still doing most of the heavy lifting. If you want the wider picture on why staying lean and active protects male health, our piece on why daily walking may be the most powerful habit in men's health covers the fundamentals.

GLP-1s and testosterone: the clearest benefit

Of the three areas in this article, testosterone has the strongest and most consistent evidence. Study after study shows that when men with obesity or type 2 diabetes lose weight on a GLP-1 drug, their testosterone climbs. Importantly, their brain hormones that drive the testicles (called LH and FSH) tend to rise too, which suggests the whole system is waking back up rather than being artificially propped up.

Real-world data tell the same story. At a 2025 endocrinology meeting, researchers reported that in a group of men with obesity and type 2 diabetes, roughly 10% weight loss over 18 months lifted the share of men with normal testosterone from around half to more than three quarters. A separate 2025 pilot using tirzepatide reported that low testosterone was reversed in every treated man over two months, with bigger gains than a testosterone gel.

Two honest caveats. First, these benefits show up in men who are overweight or metabolically unwell. In lean, healthy men, GLP-1 drugs do not appear to boost testosterone. Second, some of the individual studies are small and short. The direction of travel is convincing, but the field still lacks large, long trials designed specifically around men's hormones. If you want to understand which testosterone numbers actually matter, our guide on the metrics you should know is a good next read. A home saliva test for free testosterone, the Testometer, is also coming soon from Adam Health.

Why GLP-1s beat TRT if you want kids

This is the point that surprises most men, and it is arguably the most useful thing in this article. Testosterone replacement therapy (TRT) works by adding testosterone from outside the body. It reliably lifts your levels and can make you feel better. But your body notices the outside supply and responds by switching off its own production line. The same brain signals that drive your testicles to make testosterone also drive them to make sperm. Turn those signals down and sperm production can fall sharply, sometimes all the way to zero.

GLP-1 drugs do the opposite. Because they lift testosterone indirectly, by fixing the metabolic problem rather than replacing the hormone, your own production line keeps running. In head-to-head studies, GLP-1 treatment raised testosterone while preserving or increasing the brain hormones that support sperm, whereas TRT raised testosterone but suppressed them.

For a reproductive-age man with obesity-related low testosterone who wants children, that is a genuinely different set of trade-offs. It does not make GLP-1 drugs a fertility treatment, and it does not mean TRT is wrong for everyone. Plenty of men are not trying to conceive and do very well on properly managed therapy. But if fatherhood is on the horizon, the choice matters. Our explainer on how long testosterone therapy takes to work is worth reading before you start any hormone treatment.

GLP-1s and fertility: promising but early

Here the evidence is thinner, and honesty is the right policy. There are good reasons to expect fertility to improve when an obese man loses significant weight. Excess weight is linked to lower sperm count, weaker motility (how well sperm swim) and worse shape, so reversing it should help. Early studies broadly support this.

Laboratory work adds a plausible mechanism. Scientists have confirmed that GLP-1 receptors are present in the human testicle, and animal studies suggest GLP-1 signalling can improve sperm movement and reduce sperm DNA damage. That said, we should not over-read this. The human studies are small, short and heavily influenced by weight loss itself rather than any special sperm-repairing power of the drug. There are no large studies yet showing that men on GLP-1 drugs go on to father more children.

So the fair summary is this. For an overweight man, losing weight on a GLP-1 drug is likely to be good news for sperm quality, mostly because losing weight is good news for sperm quality. Anyone who wants to see this play out should measure the full picture, including erections, which are one of the most sensitive early signals of vascular and hormonal health.

The one big caveat: trying for a baby

There is one safety point that everyone on these drugs should know. GLP-1 medicines have shown harm to developing offspring in animal studies, and there is very little human safety data in pregnancy. For that reason, the official advice is to stop GLP-1 drugs before conception. Because the drug takes several weeks to clear the body, the usual guidance is to stop around two months before trying.

This advice is aimed mainly at women, because the concern is about the developing pregnancy. For men, there is no established evidence that GLP-1 drugs damage sperm or harm a future pregnancy through the father. Encouragingly, a large safety database review did not flag GLP-1 drugs among the medicines most linked to male fertility problems. But the male side of this question is simply understudied, so it is not something to guess about on your own.

GLP-1s and erections: a mixed picture

Most of the evidence suggests erections improve on GLP-1 drugs, but this is the area with the clearest disagreement between studies, so it deserves a careful read. The reasons to expect improvement are strong. Weight loss, better blood sugar and higher testosterone all support the health of the blood vessels that make an erection possible. Erections are fundamentally a plumbing event: they depend on the lining of your blood vessels releasing nitric oxide, a molecule that tells the arteries to relax and let blood flow in.

The largest and best-quality dataset comes from a major diabetes trial. Among more than 3,700 men, those on a GLP-1 drug had a modest but real reduction in moderate to severe erectile dysfunction compared with placebo. Other cohort studies and a genetic analysis point the same way, and animal research shows GLP-1 treatment can restore nitric oxide function in the erectile tissue of diabetic rats.

Now the other side. A 2024 database study of non-diabetic obese men found a higher rate of new erectile dysfunction on semaglutide, and a 2026 analysis in men with diabetes also reported a modestly higher rate, though that signal weakened once the researchers corrected for bias. Meanwhile a separate safety-reporting review found no unusual signal at all. Taken together, the likeliest reading is that GLP-1 drugs help erections on average, mainly through weight loss and metabolic repair, but the story is not clean and individual responses vary. You can read more about what healthy erections actually indicate in our guide to night-time erections and why you should care about them. And because those blood-vessel changes lean so heavily on nitric oxide, the same molecule is where many erection-support supplements aim.

Don't lose the muscle

One men's-health downside deserves attention: muscle. Any fast weight loss costs you some lean tissue, and GLP-1 drugs are no exception. A 2025 review of nine trials found that roughly a third of the total weight lost on GLP-1 drugs was lean mass rather than fat, though this varied by drug and by whether people trained.

Losing muscle matters for more than looks. Muscle is where a lot of your blood sugar gets handled, it supports metabolism, and it is closely tied to long-term strength, mobility and healthy ageing. Losing it defeats part of the point of getting healthier. The good news is that muscle loss is largely preventable.

• Lift something heavy, regularly. Resistance training is the single most effective way to hold on to muscle while you lose fat. Two or three sessions a week is enough to make a real difference.
• Eat enough protein. As calories drop, protein becomes more important, not less, because it gives your body the raw material to protect muscle.
• Go at a sensible pace. Faster is not always better. Very rapid loss tends to cost more lean mass.

Some doctors now deliberately pair GLP-1 drugs with strength training, and in select cases with testosterone therapy, specifically to protect muscle. The theme running through all of this is the same one that runs through everything at Adam Health: the only way to know whether your plan is working is to measure it, not to guess.