Millions of Britons taking weight-loss jabs may need to stay on them for life, experts have warned.
A landmark study found most users regain the weight inside two years of stopping treatment, much faster than traditional dieters.
The injections, including now-household names such as Mounjaro and Wegovy, have been hailed as a breakthrough in obesity treatment.
But a major Oxford review suggests the benefits may be short-lived once treatment ends.
In the first analysis of its kind, examining 37 studies involving more than 9,300 people, researchers found that when the jabs are stopped, weight returns rapidly – regardless of how much was lost.
On average, users gained around a pound a month after quitting, with many projected to have regained much of or all the weight lost by between 17 and 20 months.
Professor Susan Jebb, co-author of the study and adviser to ministers and the NHS on obesity, suggested people may need a lifetime solution – such as jabs or behaviour change support or both – to tackle obesity in the long-term.
She said: ‘Obesity is a chronic relapsing condition, and I think one would expect that these treatments need to be continued for life, just in the same way as blood pressure medication.’
Researchers found that stopping weight loss drugs resulted in total weight regain and reversal of heart health markers in less than two years
‘We should see this as a chronic treatment for a chronic condition,’ she added.
Writing in The British Medical Journal, the researchers warned that stopping the drugs does not just reverse weight loss but is also linked to a reversal of key heart-health benefits.
Weight returned around four times faster than in people who slimmed down through diet and exercise alone.
The findings are likely to raise questions about current NHS policy, under which Wegovy is offered for a limited period of up to two years.
Yet most patients access the jabs privately, often paying up to £300 a month, raising concerns about the cost of long-term treatment if the drugs need to be taken indefinitely.
The jabs, known collectively as GLP-1 drugs, work by mimicking hormones released after eating.
However, experts warn that withdrawing this hormonal ‘fix’ can leave users vulnerable to rebound hunger.
‘As soon as the drug is stopped, appetite is no longer kept in check,’ said Dr Adam Collins, an associate professor of nutrition who was not involved in the study.
Join the debate
Should weight-loss jabs really come with a lifetime price tag?
‘If people haven’t built sustainable habits alongside treatment, going cold turkey can be extremely difficult – and some may regain even more weight than they lost.’
The researchers analysed studies comparing all licensed weight-loss medications – including newer GLP-1 injections – with behavioural weight-loss programmes.
On average, those using jabs lose almost two-and-a-half stone (14.7kg) within nine to 12 months, but typically regained around a pound (0.4kg) a month after stopping and were projected to return to their pre-treatment weight within two years.
Cardiometabolic benefits – one of the drugs’ major selling points – also faded, with improvements in blood sugar, blood pressure and cholesterol returning to pre-treatment levels in under 18 months.
Those who relied on diet and exercise programmes alone lost less weight – around 5kg on average in studies lasting a year – but regained it much more gradually, putting on just a fifth of a pound (0.1kg) a month.
In this group, cardiometabolic benefits persisted for up to five years after the programme ended.
Around 2.5million people are currently thought to be using new GLP-1 drugs in the UK.
Professor Jebb added: ‘What we’ve shown is that weight regain after treatment is common and rapid – suggesting the jabs should not be seen as a short-term solution.
‘In the real world we know that adherence is surprisingly poor, with around half of people discontinuing these medications within a year.’
Two in three Britons are now classed as overweight or obese, while NHS figures show adults weigh roughly a stone more than they did 30 years ago – a trend estimated to cost the economy £100 billion a year.
Under current NHS rules, only patients with a BMI over 35 and a weight-related health condition – or those with a BMI between 30 and 34.9 referred to specialist services – should receive the drugs.
However, more than half of local health commissioners in England are expected to tighten access amid cost concerns.
Obesity has been linked to at least 13 types of cancer and is the second biggest cause of the disease in the UK, according to Cancer Research UK. It has also fuelled a 39 per cent rise in type 2 diabetes among under-40s, with 168,000 young Britons now living with the condition.
The arrival of GLP-1 drugs has transformed obesity treatment, offering dramatic weight loss that was largely out of reach with diet and exercise alone.
Concerns have been raised about the risks of the medicines, which can cause nausea, vomiting and diarrhoea, and in rare cases have been linked to pancreatitis, but experts say the benefits far outweigh the risks for most patients.
Professor John Wilding, an honorary consultant physician in cardiovascular and metabolic medicine at the University of Liverpool, said the findings were ‘not surprising’.
‘We don’t expect treatments for diabetes, high blood pressure or high cholesterol to continue working once medication is withdrawn – and there’s no scientific reason obesity should be different,’ he said.
‘These drugs should be considered long-term treatments, not a quick fix.’