Weight-loss jabs: the side effects nobody mentions
Weight-loss jabs can take away more than your appetite. Here’s what they do to mood, pleasure, muscle and your social life, what the evidence says, and when to get help.
Reviewed, edited and approved by Editor-in-chief Daniel Sköld · Updated 24 October 2026
Contents
The headlines about Wegovy and Mounjaro tend to cover two things: the impressive weight loss and the nausea. Both are real. But talk to men who’ve been on a weight-loss jab for a few months and you’ll hear about some quieter changes. The pint that no longer tastes of anything much. The Sunday roast you push around the plate. A flatness that’s hard to put into words.
None of this means the drugs are dangerous or that you shouldn’t take one. It means you should know what you’re signing up for, and which changes are worth a word with your GP or pharmacist.
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What are the common side effects of weight-loss injections?
Let’s start with the stuff in the leaflet. Semaglutide (Wegovy) and tirzepatide (Mounjaro) slow down how fast your stomach empties and act on the parts of the brain that control appetite. Not surprisingly, most of the common side effects are in your gut: feeling sick, being sick, diarrhoea, constipation, indigestion and bloating. Tiredness, headaches and dizziness are common too, especially in the early weeks and after each dose increase.
For most people these ease off as the body adjusts. Eating smaller meals, stopping when you’re full, going easy on fatty food and drinking enough water all help. If you’re being sick a lot, though, you can get dehydrated, and that’s hard on the kidneys. Don’t just put up with it. Speak to whoever prescribed the jab.
Then there are the rare but serious ones. Severe stomach pain that won’t go away, sometimes spreading to your back, can be a sign of pancreatitis and needs urgent medical help. Pain in the upper right side of your tummy, a fever or yellowing skin or eyes can point to gallbladder trouble, which is more likely with rapid weight loss. If you’re due to have an operation or a procedure under sedation, tell the team you’re on a jab, because a slow-emptying stomach matters under anaesthetic.
Can GLP-1 drugs make you feel depressed or flat?
This is the question behind a lot of nervous forum posts. In 2023 European and UK regulators started looking into reports of depression, self-harm and suicidal thoughts in people taking GLP-1 drugs. The European Medicines Agency reported its findings in April 2024, and the MHRA followed in September 2024. Both reached the same conclusion: the evidence doesn’t show that the drugs cause suicidal thoughts, self-harm or depression. The MHRA said it would keep monitoring, and some experts still want better research, especially in people who already have a mental health condition.
That’s reassuring, but it isn’t the whole story. A regulator finding no proof of a causal link is not the same as saying nobody ever feels low on these drugs. Losing weight quickly, eating far less and feeling sick a lot can drag anyone’s mood down. And people who start a jab often bring a long history with food, weight and self-esteem along with them.
The more interesting idea, and the evidence here is still early and mostly anecdotal, is about pleasure. GLP-1 receptors are found in the brain’s reward system, not just the appetite centres. That’s thought to be part of why the drugs quieten the constant mental chatter about food that many users call “food noise”. Researchers are also studying whether the jabs could reduce cravings for alcohol and other addictive substances. The obvious next question is whether, for some people, the dial on everyday enjoyment gets turned down too. Some users describe exactly that. Proper studies haven’t yet shown whether it’s a real drug effect, and if so how common it is.
A jab that quietens your appetite is doing its job. A jab that quietens your enjoyment of life is something to tell your GP about.
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The social side effect: when the pub loses its appeal
Here’s one you won’t find in any leaflet. A lot of male social life in Britain revolves around food and drink: the curry after five-a-side, the pint with your brother, the barbecue. If you suddenly can’t face more than half a burger and two sips of bitter, you may find yourself saying no to invitations, or turning up and feeling like a spare part.
Some men are glad of it. Others find they’ve lost some of what made the week enjoyable without anything taking its place. The fix isn’t to quit the jab. It’s to build some social plans that don’t centre on eating: a walk, parkrun, a round of golf, the shed. Tell your mates what’s going on, too. It saves a lot of “you’re not drinking?” at the bar.
Will I lose muscle on Wegovy or Mounjaro?
Probably some, yes. When you lose weight quickly by any method, part of what goes is lean tissue, muscle included, not just fat. For men in their late forties and fifties, who are already losing muscle with age, that matters. Less muscle means less strength, a slower metabolism and, further down the line, more risk of falls.
The answer is not complicated. Do some resistance training at least twice a week, as the UK physical activity guidelines recommend: weights, resistance bands, bodyweight exercises or heavy gardening all count. Make sure there’s decent protein in the smaller meals you are eating. A dietitian or your weight management service can help if you’re unsure. Some people also notice thinning hair during rapid weight loss. It’s usually temporary, but mention it if it bothers you.
What to do if the jab is getting you down
Don’t stop or change your dose on your own. Book a GP appointment, or speak to the prescribing pharmacist if you went private, and be specific. “I’ve felt flat for six weeks and I’ve stopped seeing friends” gets you further than “I’m a bit off”. There may be a simple fix, such as staying on a lower dose for longer, or the problem may have nothing to do with the jab at all.
If you’re having thoughts of harming yourself, don’t wait for an appointment. Call NHS 111, or contact Samaritans free on 116 123 at any hour. In an emergency, call 999. You can also report any suspected side effect yourself through the MHRA’s Yellow Card scheme. Reports from patients are how regulators pick up problems that clinical trials miss.
And get your jab from a proper source. Mounjaro is available on the NHS in England for some patients with the greatest clinical need, with access in Scotland, Wales and Northern Ireland handled by their own health services. Privately, buy only from a registered UK pharmacy that checks your medical history. Pens sold through social media or beauty salons can be fake, and with those you have no idea what you’re injecting.
In short
Weight-loss jabs mostly cause gut problems, which usually ease with time, and rarely cause serious ones such as pancreatitis that need urgent help. UK and European regulators have found no evidence that they cause depression or suicidal thoughts, but some users report feeling flat or getting less pleasure out of life, muscle loss is a real risk, and the knock-on effects on your social life deserve some thought. If your mood changes, talk to your GP or pharmacist rather than stopping the drug on your own, and pair the jab with strength training and enough protein.
Adrian Irving writes about health for men 45 and over who would rather do something than worry. Training, weight loss, sleep, cholesterol and blood tests, heart health, testosterone, the prostate, mental health and your sex life – what the evidence says, what's worth trying, and when it's time to see your GP.
One of Midcent's writers. Spotted something? Write to adrian@midcent.uk.
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