GLP-1 side effects: the risks nobody mentions before your first injection

The clinic told you it’s nausea for a few weeks and then it settles down. Your mate at work who’s down 15kg said much the same. Felt rough for a fortnight, fine now, wouldn’t go back.

Nobody mentioned the eyes. In July the TGA added a warning to the Australian product information on these drugs about a rare injury to the optic nerve that can take your sight and not give it back. Nobody mentioned that the manufacturers are defending more than four thousand cases in one American court, brought by people who say the label never told them what could happen to their gut. And nobody mentioned that of every five kilos you drop, close to two of them won’t be fat.

These drugs work. Further down I’ll show you the best evidence for them rather than pretend it doesn’t exist, because I’d rather you trusted the rest of this. But the risk briefing you got wasn’t the risk briefing. If you’re 45 with a family and a business, you’re owed the real one before you put the first needle in.

What are the serious GLP-1 side effects in men over 40?

The serious GLP-1 side effects are acute pancreatitis, acute gallbladder disease, acute kidney injury, gastroparesis where the stomach stops emptying properly, and ileus where the bowel stops moving altogether. Pancreatitis means stopping the drug and getting yourself to an emergency department. Gallbladder trouble turns up because fast weight loss of any kind throws gallstones. The kidney injury usually comes from being so dehydrated by vomiting that the kidneys take a hit. The American regulator added ileus to the Ozempic label back in September 2023, once enough reports had come in.

The common side effects are the gastrointestinal ones, and most men get some of them: nausea, vomiting, diarrhoea, constipation, abdominal pain, reflux, headache, fatigue. They’re worst through the sixteen to twenty weeks you spend climbing the dose. That’s the part you were told about, and for most men it does settle.

Then there’s one almost nobody hears about until it’s a problem. These drugs slow how fast your stomach empties, that’s the whole mechanism, so there can be food sitting in there when a surgeon is assuming there isn’t. That raises the risk of aspiration under a general anaesthetic. Surgery booked, a colonoscopy, dental work under sedation: your anaesthetist needs to know weeks ahead, and nobody is going to chase you for it. You raise it.

One hard contraindication: a personal or family history of medullary thyroid carcinoma, or MEN 2, and these drugs are off the table entirely. Regulators have also asked prescribers to watch men with a history of depression more closely.

So how much do the serious ones actually go up? The number everyone quotes is a 2023 JAMA cohort study, Sodhi and colleagues, pulled from a sample of 16 million patient records, comparing people using GLP-1s for weight loss against people using bupropion-naltrexone, an older weight-loss drug. Pancreatitis came out around nine times higher. Bowel obstruction around four. Gastroparesis around three and a half.

Those figures are softer than they look. The confidence interval on the pancreatitis one runs from 1.25 to 66, which tells you almost nothing about the size of the effect, and nine has no particular claim on being the truth. The gastroparesis figure has a different problem, which is that a doctor is quicker to write down delayed stomach emptying in a patient who’s taking a drug famous for delaying stomach emptying. Bigger analyses since haven’t found a pancreatitis signal anything like that size. I’ll keep using Sodhi, because it’s the most cited work we’ve got, but I won’t hand it to you as settled science when it isn’t.

These events are rare.

The TGA added a vision-loss warning to GLP-1 product information in July 2026

In July 2026 the TGA updated the Australian product information for GLP-1 medicines to warn about non-arteritic anterior ischaemic optic neuropathy. NAION. It’s a loss of blood supply to the optic nerve, and it turns up suddenly, usually in one eye, usually noticed on waking, and it doesn’t hurt. The no-pain part is why a man leaves it a couple of days. In the TGA’s own words it may result in permanent visual impairment, including blindness, and no treatment has been shown to improve visual acuity outcomes.

Sitting behind that decision were 36 reports of the condition on the national adverse events database in people taking these drugs. Twenty-three on semaglutide, ten on tirzepatide, three on liraglutide. A reporting database like that has no denominator, so those 36 tell you the events got noticed and flagged. They don’t give you a rate and they don’t prove the drug did it.

Europe’s numbers are the ones I’d hold onto. In June 2025 the European Medicines Agency’s safety committee called NAION a very rare side effect of semaglutide, meaning it may affect up to 1 in 10,000 people taking it. Large studies in type 2 diabetes put the risk at roughly double that of people not on the drug, which works out to about one extra case per 10,000 person-years of treatment. Their instruction to patients was blunt: sudden loss of vision, or eyesight going downhill fast, ring your doctor that day. Confirmed NAION, the semaglutide stops.

The science here is still being argued and you should have that too. The established risk factors for NAION are diabetes, high blood pressure, sleep apnoea, being over 50. Which is a description of the men who get prescribed these drugs. So when a study finds semaglutide users getting more NAION, part of that might be the drug and part of it might be that sicker men take the drug. A Danish and Norwegian cohort found the risk close to tripled after adjustment. A different cohort, matched for age, blood pressure, diabetes, sleep apnoea and heart disease, found no significant increase at all. Regulators moved anyway, on the view that something permanent and untreatable earns a warning while the argument runs.

Hold both halves of that, because the internet will only sell you one. Very rare is genuinely very rare. Permanent is genuinely permanent. You’re being asked to take a small chance on something that can’t be undone, and honest consent says that out loud instead of rounding it down to some blokes get a bit queasy.

Why are more than 4,000 people suing over GLP-1 drugs?

Because they say they weren’t warned. As of 1 September 2026 there were 4,022 cases pending in MDL 3094, the consolidated gastrointestinal-injury litigation in the Eastern District of Pennsylvania, before Judge Karen Marston. Around 75% of those complaints involve gastroparesis, about 18% ileus, about 8% gallbladder injuries. There’s a second, separate proceeding, MDL 3163, consolidated in December 2025 for the vision-loss claims, with 216 cases pending by September 2026. The claims are failure to warn, design defect, breach of warranty.

That’s a big number and it’s worth less than it looks. None of those cases has been to trial. There’s no settlement in either proceeding. A filed claim is an allegation and plenty of allegations go nowhere. The size of a mass tort also tracks how hard the plaintiff firms are advertising: they buy the ads, aggregate the leads, the docket grows. Four thousand filings tells you there’s a legal market here before it tells you anything about your gut.

Use it for one thing. Those cases exist because a lot of people say the information they got beforehand didn’t describe what happened to them afterwards. You’re standing on the same side of that gap right now, holding the same brochure.

Muscle loss is the GLP-1 side effect that isn’t on the label

In the STEP 1 semaglutide body-composition substudy, participants lost about 19% of their fat mass and about 10% of their lean mass. Run those two together and lean tissue was roughly 39% of everything that came off the scale. Across the trials the range lands around 25% to 40%. So of every five kilos, close to two of them are not fat.

Here’s the part the drug companies don’t have to defend, and I won’t pretend otherwise: the injection isn’t doing this to you. Fast weight loss does it, on any method, mine included. The DIETFITS trial was food only, with a low-carb arm not far off how I feed my clients, and when they measured body composition by sex the men gave up a significantly higher share of lean tissue than the women did. No reason a needle changes that arithmetic in either direction.

You know why it lands harder at 50 than at 30. From your forties on you’re losing muscle every year anyway, so there’s no buffer sitting there. And muscle is where you burn fuel, it’s where insulin sensitivity lives. Take a few kilos of it off a man and you’ve made the engine smaller in the body that now has to hold this result, which is a strange thing to do a few months before you hand that body its appetite back. I’ve written up what that does afterwards in what actually happens when you stop a GLP-1.

The drug doesn’t eat your muscle. It just arrives with nobody attached to it whose job is to stop that happening. A script won’t check your protein. It won’t put a barbell in your hands twice a week. That’s the gap, and it’s the only bit of this a coach can actually do anything about.

Do GLP-1 drugs have proven benefits beyond weight loss?

Yes, and for one group of men the evidence is strong enough that I’d be wrong to argue with it. The SELECT trial randomised 17,604 people who were overweight or obese, with established cardiovascular disease and no diabetes, to semaglutide or placebo. Major cardiovascular events hit 6.5% of the semaglutide group against 8.0% on placebo, over a mean of a bit over three years. A fifth lower in relative terms, a percentage point and a half in absolute terms. That’s a hard outcome in a big randomised trial. It’s why the TGA registered Wegovy for cardiovascular risk reduction in December 2024.

Nothing else in this article outranks that. If you’ve got established heart disease, that trial is a serious reason to be on this drug, and the conversation belongs with a cardiologist rather than with me.

Your GP might also put this to you, and it’s a fair hit: nobody says a blood pressure tablet doesn’t work because people stop taking it, so why judge this one on what happens when you quit. Three answers. None of these drugs are subsidised on the PBS for weight loss here, so unlike the blood pressure tablet you’re funding this yourself, indefinitely. The muscle bill accrues the whole time you’re on it, not just at the end. And the way you eat, which is what put the weight on in the first place, is still sitting there waiting. So keep taking it if that’s the call you make with your doctor. Just spend the room it’s buying you on something that lasts.

Are you accepting permanent risks for temporary weight loss?

For a lot of men, yes, and it’s the trade nobody sets out for them. The pancreatitis risk, the gallbladder risk, the small chance of an optic-nerve injury you can’t reverse: none of that expires when the prescription does. The weight loss does. Up to about 65% of men without type 2 diabetes stop inside a year, mostly on cost and tolerance, and around two-thirds of what they lost is back within twelve months of stopping. I’ve gone through why that happens in life after Ozempic, why the weight comes back.

Be precise about what that means, because it’s a claim about adherence and not about whether the drug works. Stay on it and it keeps working. The question is whether you’re going to stay on it at $400 a month, unsubsidised, for the next twenty years. Most men, asked plainly, say no.

The money belongs in the risk column too. Ozempic prescribed off-label runs roughly $130 to $200 a month. Wegovy is roughly $350 to $450 at the maintenance dose. Mounjaro runs roughly $345 to $645 depending on the dose. Call it a car service every month, for something that hands the weight back when you stop paying.

Mark, a consultant on the Sunshine Coast, came at this from the surgical version of the same fork. His GP had referred him for weight loss surgery and he was three months into the waiting list, so we started while he waited. Twelve weeks later he was 18kg down, it kept going to 20kg, and he never had the operation. He wasn’t braver than anyone else, he just got a proper look at the irreversible option before he committed to it.

How to protect your muscle while you’re on a GLP-1

If you’re already on one and it’s working, you’re not the man I’m arguing with, and you don’t need talking out of anything. You’ve got a result and a window. This is what the window is for.

The dose is doing one job. It’s holding your appetite down. It isn’t building the way you eat, the protein floor, or the muscle that has to hold this weight when you stop. So build those three while the drug is still doing its job.

Protein first, weighed rather than guessed. The research targets sit at roughly 1.6g or more per kilogram of body weight a day for a man losing weight fast, which for a 120kg bloke is close to 190g, against an appetite that’s been cut by around 40%. That’s hard. That’s the whole point. It’s also a conversation for your prescriber and a dietitian rather than something to wing, because deficiencies are common on these drugs: in one claims analysis of 461,382 adults newly prescribed a GLP-1, 22% picked up a nutritional deficiency diagnosis inside twelve months, vitamin D most often.

Then two resistance sessions a week, getting heavier over time rather than longer. Normally I’m relaxed about this. Only about 10% of my clients do any gym work while they’re losing weight and I’m usually happy with walking, a standing desk and 15,000 steps a day. On a GLP-1 it changes, because you’re dropping weight faster than food alone would and the lean tissue goes with it. If you haven’t lifted in a decade, get a physio or a trainer for technique first.

Then a way of eating you’d still be on at $0 a month. And get a body-composition read now, not at the end, because the scale can’t tell you whether that 12kg was fat or engine.

Do all that and the taper is a non-event. Skip it and you’ll be back here in three years at the same weight you are now, carrying less muscle than you’ve got today.

Appetite is a food problem before it’s a drug problem

A GLP-1 turns the appetite signal down. It doesn’t touch what’s producing the signal, which is a diet built on processed carbohydrate that spikes your blood sugar, drops it, and has you in the pantry at 3pm. Take the processed carbohydrate out, get fat-adapted, and the appestat starts regulating itself without an injection. For a man who genuinely can’t stop eating, having that switched off isn’t a small thing, and I’ll grant it completely.

We don’t put on weight because we eat too much red meat or too much fat. We put it on because we’ve got too much insulin, and insulin goes up when the sugar goes in.

Richard shows the mechanism rather than the choice, because he never faced this decision. He came to me from the UK, weekly video call, and lost 18kg in twelve weeks with walking as his only exercise. He cut the sugar and the processed food, he ate more than he had been, and what he said afterwards was that he didn’t crave food any more. That’s appetite suppression out of a kitchen, with no script involved.

It’s also why I’d run him differently today. He didn’t lose 18kg without giving up some lean tissue, and nobody put him on a DXA to find out how much. Fast loss without lifting has a bill attached whether a drug is involved or not. That’s my own argument turned back on my own work, and it holds up.

If you have to inject a hormone to stop yourself eating, the food is doing something to you that it shouldn’t be. For most of the men I see, changing what’s on the plate takes the hunger away and the drug question never comes up. For some it won’t be enough, and I’ve met them. Fix the food while you’re on the drug and you get to keep the result after you stop. Fix nothing and you’re renting a smaller body at $400 a month and handing it back the day you stop paying.

You should know where I’m standing while I say all this. I sell the alternative. I coach men one to one for a living and I don’t write prescriptions, so read every word above with that in your hand. It’s also why I’ve quoted the regulators and the trials instead of my own opinion, and why I’ve told you where those numbers are weak. Go and check them, the links are at the bottom. If you want the decision itself laid out from both sides, I did that in GLP-1 or a health coach.

Two different men have read this far. If you haven’t started, your question is whether you need it at all. If you’re on it and it’s working, your question is what has to be true before the dose comes down. Same thirty minutes either way: your actual week, what you eat, what you drink, how you sleep, what you lift, where your protein sits right now. I won’t talk you off a script and I won’t talk you onto one. You’ll leave with three things written down: the one thing actually driving your appetite, the protein and training floor you need at your bodyweight, and the order I’d taper in so the weight doesn’t follow the dose back up. Then go and fix it, with me or without me.

This is 1-on-1 coaching, weekly calls and a daily food log, for men with 10kg or more to lose who want the oversight and not just the information. If that’s you, let’s talk.

Frequently Asked Questions

What are the worst side effects of Ozempic?

The serious ones are acute pancreatitis, gallbladder disease, acute kidney injury from dehydration, gastroparesis where the stomach stops emptying, and ileus where the bowel stops moving. Since July 2026 the Australian product information also warns about NAION, an optic-nerve injury that can cause permanent vision loss. There’s also a raised risk of aspiration under general anaesthetic because the drug slows gastric emptying, so tell your anaesthetist before any procedure.

Can Ozempic really cause blindness?

It can cause NAION, a sudden loss of blood supply to the optic nerve that may result in permanent visual impairment including blindness, and no treatment has been shown to improve the outcome. It’s very rare. The European Medicines Agency put it at up to 1 in 10,000 people on semaglutide, roughly double the background risk, or about one extra case per 10,000 person-years. The causal link is still contested, because diabetes, high blood pressure and sleep apnoea raise NAION risk on their own and those are the men who get prescribed these drugs.

Why are people suing over Ozempic and Mounjaro?

They allege the manufacturers failed to warn them about severe gastrointestinal injuries and vision loss. As of 1 September 2026, 4,022 gastrointestinal cases were pending in MDL 3094 in the Eastern District of Pennsylvania, about 75% of them involving gastroparesis, plus 216 vision-loss cases in the separate MDL 3163. No case has gone to trial and there’s no settlement, so these are allegations rather than findings, and mass-tort case counts also track how much law firms spend advertising for claimants.

Does Ozempic cause stomach paralysis?

Gastroparesis, or delayed stomach emptying, is a recognised risk and it’s the injury named in about three quarters of the US lawsuits. A 2023 JAMA cohort study found the risk roughly three and a half times higher in people using GLP-1s for weight loss than in people using bupropion-naltrexone, though the case numbers were small and doctors are quicker to code delayed emptying in a patient taking a drug known to delay it. The drug slows gastric emptying by design, which is how it makes you feel full.

Do you lose muscle on Ozempic?

Yes, and more than most men expect. In the STEP 1 body-composition substudy participants lost about 19% of fat mass and about 10% of lean mass, which works out to lean tissue making up roughly 39% of the total weight lost, and across the trials the range is about 25% to 40%. That’s a tax on rapid weight loss rather than a drug effect, and dietary trials that measured it found men lose a higher share of lean tissue than women. Protein at 1.6g or more per kilogram of body weight and two resistance sessions a week are the difference between losing fat and losing your engine.

Are GLP-1 drugs safe for men over 40?

For most men they’re tolerated, and in men with established heart disease the SELECT trial showed a genuine reduction in cardiovascular events. The catch is that the serious risks can be permanent while the weight loss depends on you staying on the drug: up to 65% of men without diabetes stop within a year, and around two-thirds of the weight returns within twelve months of stopping. If you use one, use it with protein, resistance training and a food pattern that can hold on its own afterwards.