Pros and cons of weight-loss jabs

still life shot of a pack of Ozempic with the injector pen in the foreground

If you're not obese or diabetic, experts have 'no idea' if the benefits of weight-loss jabs outweigh the risks

(Image credit: Steve Christo / Corbis via Getty Images)

published 6 February 2025

Just one injection a week and down goes that dial on the scales. Weight-loss jabs, such as Ozempic, Wegovy and Mounjaro, have quickly earned a glowing global reputation for shifting the pounds – especially among the rich and famous. So many of the UK's wealthy now get the jabs on private prescription, Savile Row tailors are overrun with requests to "radically" readjust bespoke suits and shirts to fit "newly svelte frames", said The Times.

The medications in these "skinny jabs" are glucagon-like peptide-1 receptor agonists (GLP-1RAs) – a group of drugs, usually semaglutide (Ozempic, Wegovy) or tirzepatide (Mounjaro), that mimic the way the hormone glucagon-like peptide-1 (GLP-1) works in the body to regulate blood-sugar levels, slow digestion and reduce appetite. NHS GPs can prescribe Wegovy (and, from April, Mounjaro) for weight loss, and both Mounjaro and Ozempic for type 2 diabetes – although strict obesity eligibility criteria apply.

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There's plenty of evidence that, if you've got pounds to shift, GLP-1RA jabs will shift them. One clinical trial in 2021, involving almost 2,000 obese people, showed those taking Wegovy lost 15% of their bodyweight in a year. And the results for Mounjaro seem even more impressive, with a Yale University study reporting losses of up to 20%. In a bonus for the gym-phobic, obesity specialists now suggest these drugs work so well, you don't even need to exercise too (as was advised with older weight-loss jabs like Saxenda). We no longer "mandate" exercise because "we see that, even without it, people are maintaining their weight loss", David Saxon, medical director of the University of Colorado Anschutz Medical Campus, told The Atlantic.

Weight-loss jabs are notorious for producing "fishy burps" and "eggy breath", and studies do confirm "eructation" as a side effect. Other commonly evidenced side effects include "feeling sick, vomiting, bloating, constipation and diarrhoea", said the BBC. These unpleasant gut-related symptoms tend to be at their worst at the start of the treatment, or if you increase the dosage. They are "usually non-serious" but "can sometimes lead to more serious complications, resulting in hospitalisation", said the UK's Medicines and Healthcare Products Regulatory Agency.

GLP-1RAs already have a strong track record for treating type 2 diabetes. But the Nature Medicine study highlights a host of other health benefits. It confirms earlier research that the drugs bring a "significant boon to heart health", said the BBC. As well as a 9% reduced risk of heart attack and a 8% reduced risk of deep vein thrombosis, there are "lower levels of stroke and high blood pressure". Other, newly emerged plus points include a lower risk of pancreatic cancer, as well as "less liver cancer, muscle pain and chronic kidney disease". These effects are likely to be linked to "the health benefits of physically losing weight", the study leader Dr Ziyad al-Aly, assistant professor of medicine at Washington University, told a press conference.

Dr Aly's study also highlights some health risks previous research had not uncovered. It found that weight-loss drugs "were associated with an 11% increase in arthritis risk and a 146% higher risk of pancreatitis – an inflammation of the pancreas that can lead to life-threatening complications", said Nature. The data also shows an increasing frequency of low blood pressure and fainting, headaches, joint pain and disturbed sleep, and a 15% higher risk of kidney stones. It was "eye-opening" to see "all these different hits in different organ systems", Dr Aly told the BBC.

Perhaps what's got the scientific community most excited in recent weeks is the new evidence about the effects of weight-loss jabs on mental health. GLP-1RAs appear to reduce the risk of psychotic disorders, such as schizophrenia, by 18%, as well as decreasing the risk of suicidal intentions, self-harm and some eating disorders. Fascinatingly, they also seem to curb substance-use disorders: the "drugs act on regions in the brain that are involved in reward and impulse control", Dr Aly told Nature, so this may explain reduced cravings for tobacco, alcohol, cannabis and opioids.

GLP-1RAs curb hunger cues and remove the desire to eat, which is great for shedding pounds but can shred your relationship with food – and with the social buzz of shared eating. The way the jabs also dampen the desire to drink alcohol has already alarmed investors, with "stock picker" Terry Smith at Fundsmith recently offloading his firm's stake in drinks firm Diageo because the sector is "being impacted negatively by weight-loss drugs", said The Guardian. Could you face getting no pleasure from eating and drinking with friends? Even the "pioneer of Ozempic" thinks not: "once you've been on this for a time, life is so miserably boring that you can't stand it any longer and you have to go back to your old life", Jens Juul Holst, the Danish professor who discovered the hormone GLP-1's effects on satiety, told Wired.

People taking weight-loss injections are less likely to have cognitive disorders such as Alzheimer’s and dementia, "which could be because GLP-1RAs reduce inflammation in the brain", said BBC Science Focus. They are also less prone to seizures, bacterial infections and pneumonia. While the reduction in risk for these conditions is fairly small, at 10 to 20%, "the benefits are still significant, especially for conditions like dementia where few effective treatments are available".

All those pounds you lose with the jabs will probably pile back on once you stop. A 2022 study, published in Diabetes, Obesity and Metabolism, found that, within a year of ending weekly semaglutide injections, people regain, on average, two-thirds of the weight they had lost – with a similar reversal in their cardiometabolic health. If you therefore need to keep taking these drugs "in order to ensure that weight doesn't return", then "that's, for me, a big problem", Dr Margaret McCartney, a GP and advocate for evidence in medicine, told the BBC. And, if you're paying upwards of £37 a week for a private "skinny jab" prescription (given that NHS prescriptions are limited), forever fending off that "Ozempic rebound" comes at quite a cost.

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Helen Brown joined The Week as staff sub-editor in 2024. She edits and fact-checks articles, and also writes the odd one or two. She has a particular interest in health and sport, and has written a book on parenting. She read Classics and Modern Languages at the University of Oxford, where she wrote for the student paper, Cherwell, and then studied magazine journalism as a postgrad at City University, London. After working as a local newspaper reporter and a sports researcher for the BBC, she cut her sub-editing teeth at Radio Times, before becoming chief sub-editor at Cosmopolitan and then the health-and-fitness magazine Zest. She also wrote for The Guardian, The Independent and the Daily Mail.