Revealed: Which slimming jab REALLY works best. The doctors’ ultimate expert guide on which to pick, how to save money, beat every side effect… and what you need to know about the ‘golden dose’

They’re the medical revolution of this century, drugs that help you lose weight without a huge amount of effort.

First there were Victoza and Saxenda, then Ozempic seized the spotlight – followed by Wegovy and Mounjaro.

And the range is rapidly expanding – there are now tens of weight-loss drugs under development, with ever-better products promised soon.

CagriSema is soon to be the new drug on the block, promising the most weight loss yet – up to 23 per cent of body weight a year, compared with 16 per cent with Wegovy and 22 per cent with Mounjaro.

It combines semaglutide – the active ingredient also in Wegovy and Ozempic, which mimics glucagon-like peptide-1 (GLP-1), a key hormone produced by the intestine after you have eaten – with a new molecule called cagrilintide, which mimics the hormone amylin, which slows your stomach emptying, making you feel full for longer after eating. CagriSema is due to become available next year.

Similar results have been seen with retatrutide, developed by Eli Lilly, the maker of Mounjaro. In just 24 weeks, patients lost an average 24 per cent of body weight. Also known as ‘Triple G’, it targets GLP-1 and two other appetite hormones – GIP and glucagon – ‘increasing the efficacy of the medications’, says Alex Miras, a clinical professor of medicine at Ulster University. And there may soon be a more appealing option, a daily pill that’s also cheaper than weekly jabs.

There’s no doubt these types of drugs, which have been around for nearly 20 years to treat type 2 diabetes, can be game-changers for those with severe obesity.

As Carel Le Roux, a professor of metabolic medicine at Ulster University, explains: ‘The benefits may go beyond short-term weight loss, they may also improve heart health, combat kidney disease and lower the risk of dementia.

‘This is because the drugs reduce fat that causes problems inside specific organs, but also because the drugs have benefits beyond weight loss.’

He adds: ‘Some people are able to function in a way they haven’t for years: to do up their laces, to walk to the shops, to go back to work.’

Other benefits include cutting your desire for alcohol – ‘semaglutide dampens down the brain’s reward system, resulting in individuals no longer getting the same pleasure from drinking,’ explains Dr Mamta Joshi, an endocrinologist at Epsom and St Helier University Hospitals NHS Trust.

It can have the same effect on your desire to smoke.

But the new weight-loss jabs aren’t without risk, with potential side-effects ranging from the mild, such as nausea, diarrhoea and rotten egg burps (as the stomach empties more slowly, food remains there longer and can ferment, leading to a build-up of stinky hydrogen sulphide gas).

People have also reported worrying cosmetic changes such as ‘Ozempic face’, ‘Ozempic teeth’, even ‘Ozempic vagina’. Plus, there’s a risk of pancreatitis (an inflamed pancreas), hospitalisation and, though much more rarely, death: last year tirzepatide (the active ingredient in Mounjaro) was recorded as a contributing factor in the death of Susan McGowan, a 58-year-old nurse from North Lanarkshire.

‘Such extreme side-effects are rare, but people need to be aware that these drugs aren’t a quick-fix for someone who just wants to lose a few pounds – they should only be taken under medical supervision,’ says Dr Foteini Kavvoura, a consultant endocrinologist at the Royal Berkshire NHS Foundation Trust.

But with strict criteria for accessing these drugs on the NHS, many people are buying the drugs online – with no guarantee you’re getting the real drug. There have been reports of people in the UK needing hospital treatment after buying what turned out to be fake semaglutide from a hairdresser or ‘a friend of a friend’.

So how do you navigate the minefield of options? What can you do to avoid the side-effects? Plus, how soon are the new, even better jabs going to become available? We spoke to the experts to find out…

 HOW CAN I GET THE JABS?

There’s no doubt lots of people would like to be on weight-loss jabs – around one in five Britons has tried to get hold of weight-loss drugs over the past year, rising to one in three among 18 to 34-year-olds.

But the cost can be prohibitive, from between £99 to £370 for a month’s supply.

Add to this Eli Lilly’s recent announcement that it was upping its wholesale prices by more than 170 per cent – though it’s since been reported that the company is trying to reduce this – experts now fear the market could be flooded with fake drugs.

GETTING THEM ON THE NHS: To get them free on the NHS you have to meet strict criteria to be considered (and even then you may struggle).

For semaglutide (Wegovy), you need to have a BMI of 30 and over, and to have at least one weight-related medical condition such as high blood pressure or sleep apnoea. The BMI is lower (27.5) for people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African Caribbean family backgrounds because of their increased risk of weight-related disease at lower body weights.

Tirzepatide (Mounjaro), which was only authorised for prescription on the NHS in June, has different criteria ‘due to the large number of patients qualifying and its high cost’, explains Dr Kavvoura. There is a three-year roll-out programme, prioritising those with highest clinical need: currently you need to have a BMI of 40 and over, with at least four of the following five weight-related medical conditions: type 2 diabetes, high blood pressure, sleep apnoea, high cholesterol or cardiovascular disease. For the higher-risk ethnic groups, it’s a BMI of 37.5. The second phase of the roll-out is planned for June 2026 and expected to include patients with a BMI of 35 and over (32.5 for ethnic groups), plus the weight-related conditions.

GETTING THEM PRIVATELY: The criteria are less strict, as it’s according to the drug’s licence rather than NHS rules – under the licence you can get them if your BMI is 27 and over, and you have at least one obesity-related complication, or simply if your BMI is more than 30.

This applies to all medications licensed for obesity, including liraglutide (Saxenda), semaglutide and tirzepatide, says Professor Miras.

While some people are getting semaglutide in the form of Ozempic for obesity, it’s actually only licensed for type 2 diabetes, so is being prescribed off-label – here, the prescriber bears more responsibility should things go wrong.

FROM AN ONLINE PHARMACY: To protect yourself you should only buy from a UK pharmacy that’s registered with the General Pharmaceutical Council (GphC), says Laura Wilson, director of the Royal Pharmaceutical Society in Scotland.

This guarantees you’re receiving safe, regulated care. Some illegitimate websites look hugely convincing, so to check, click on the green cross pharmacy logo on the website and you’ll be taken through to the GPhC register, confirming it’s legitimate.

You can also search the website pharmacyregulation.org – which lists every registered pharmacy in the UK.

‘If you don’t need a prescription, there’s no address or number, or if the deal looks too good to be true – avoid it,’ says Laura Wilson.

A responsible pharmacy will ask for detailed health information such as your medical history and current medications, confirm your identity and have all this reviewed by doctors. They’ll also provide ongoing support, including how to use the medicine safely and possible side-effects.

Expect to pay between £90 and £370 for a month’s supply.

FROM A PRIVATE CLINIC: If you’re getting the drug through a private clinic the support you get should be comprehensive – including initial assessments, ongoing monitoring plus customised nutrition, exercise and lifestyle advice.

Check the clinic is registered with the Care Quality Commission: cqc.org.uk. This means it meets essential safety and quality standards.

‘If it’s not registered, you’ve no idea what you’re getting,’ adds Laura Wilson.

‘You could get something that doesn’t work at all or, worse, something containing toxins and other ingredients that could cause real harm – you may even end up in hospital.’

Expect to pay from £400 for initial consultations with a GP and a dietitian; between £169 and £375 per month for the medication; and from £170 for follow-up appointments with a GP and dietitian.

WHEN WILL I START TO LOSE WEIGHT?

You could start to see results almost within days, although not everyone will (see below).

‘The mechanism behind all of these drugs is simple,’ says Professor Le Roux, ‘they make you feel fuller for longer and reduce your appetite’.

They work by mimicking GLP-1. This hormone stimulates insulin secretion and slows down the rate food is digested. This in turn acts in the brain on the reward system to reduce hunger and to signal feelings of fullness.

‘It doesn’t change the appeal of food, just the intense desire for it; as patients say, it quietens “food noise”,’ adds Professor Le Roux.

Because of this you eat less – calorie intake can drop by 70 per cent for the first few months, then levels out to 30 per cent from six months.

However, this can mean you miss out on important nutrients, and protein (more on protein later).

The food industry is now starting to market ranges of foods specifically designed to ‘complement’ these drugs.

Last year, Nestle became the first major food company to launch an entirely new brand, Vital Pursuit, targeted specifically at patients on semaglutide.

The range, currently only available in the US, is designed to provide ‘dietary support to GLP-1 users and consumers focused on weight management’ and features frozen meals such as cauliflower crust three-meat pizza, and chicken spinach and artichoke sandwich melt. All meals contain at least 20g of protein.

In addition, in June this year it launched ‘Boost Advanced’ – shakes said to ‘meet science-based nutritional recommendations for users of GLP-1 receptor agonists’. They contain 35g of protein to help ‘preserve muscles during weight loss, along with a special blend of nutrients designed to support digestive health and energy metabolism’.

HOW CAN I TELL IT’S NOT GOING TO WORK FOR ME?

Although the drugs can work for large numbers of people, they don’t work for some.

If the weight loss is less than 5 per cent after three months, you’re known as a ‘non-responder’, which accounts for about 5 to 8 per cent of people, says Professor Le Roux.

Why this happens isn’t clear, adds Professor Miras. ‘We suspect it has to do with the way the drug interacts with the GLP-1 receptor in the brain – i.e. how well the key interacts with the lock. If the key enters the lock well then we have a good result and the other way round.’

Professor Le Roux adds: ‘We have zero ability to predict who will fall into this camp.’

CAN I AVOID THE SIDE-EFFECTS?

‘OZEMPIC FACE’

While the weight loss may be welcome, gaunt, sallow-looking skin is less so. Known as ‘Ozempic face’ this is actually nothing to do with the medication and ‘all to do with the rapid weight loss’, says Dr Sharon Wong, a dermatologist in London and spokeswoman for the British Association of Dermatologists.

‘The loss of fat and collagen in the skin – and elasticity – results in a more sunken appearance, with noticeable sagging and wrinkles. This is a particularly common side-effect when people maximise their dose in an effort to achieve weight goals quickly – however the faster you do this, the more likely the so-called Ozempic face will appear,’ she adds.

‘To minimise the loss, lose weight gradually – ideally 1-2lb per week; this gives skin time to adapt, protects muscle and reduces the risk of sagging,’ says Charlotte Foster, a dietitian at Barts NHS Trust.

Your diet is also important, as your appetite is reduced, you need to ensure that what you do eat is nutrient dense, such as fruits, vegetables, wholegrains, oily fish, beans and lentils, she explains.

‘Keep hydrated, too. Water is vital for skin elasticity, digestion, energy and overall health.’

London-based dietitian Emer Delaney adds: ‘Most important is protein – aim for around 1-1.5g per kg body weight per day.’

LOSING TOO MUCH MUSCLE

A significant amount of the weight you lose is muscle – not fat. This is important as muscles burn calories when you’re at rest, too.

Muscle loss with GLP-1 drugs ranges from 25 per cent to 39 per cent of the total weight lost over 36-72 weeks, reported The Lancet Diabetes & Endocrinology journal last year. This is several times greater than muscle loss you’d expect through simple ageing past 40.

‘The reduced diet and nutrients mean muscle proteins break down faster than they can be built,’ says Dr Kavvoura.

‘It has a knock-on effect on bones too; when weight loss is extreme and quick, we lose fat from inside our bones, just in the same way we lose fat from other areas.’

Muscle mass is not only vital for your metabolism – but also for muscle strength and independence, particularly as we age.

To minimise the loss, make sure you eat plenty of protein.

‘As well as meat, good sources of protein include eggs, beans, seafood, cheese, peas and nuts,’ says Emer Delaney.

‘The calorie restriction can make it difficult to consume the ideal amount so adding additional protein powder to a small pot of high-protein yoghurt – can really help.’

Professor Le Roux adds: ‘Muscle loss can also be limited by exercise – particularly important in those over the age of 50, when you’re losing muscle anyway.

‘Resistance training such as squats, lunges, weight-lifting – even lifting water bottles in each arm – can help.’

‘OZEMPIC VAGINA’

That gaunt, saggy-skinned look that affects the face, can also affect the labia or vagina as a result of rapid weight loss. ‘Rapid weight loss on any body part can affect the skin over the fatty tissue lost – including the lower belly, mons pubis, and inner and outer labia,’ says Dr Sherry Ross, an associate professor of urology at the University of North Carolina.

While anyone can be affected by it, those more prone to the condition tend to be older women, whose skin has already lost its elasticity.

PANCREATITIS

Clinical trials have shown users of GLP-1 drugs have a higher risk of pancreatitis – inflammation of the pancreas – possibly due to an overgrowth of cells in the pancreas.

‘Pancreatic inflammation is dangerous because the inflammatory process can cause complications such as cell death in the pancreas itself, potentially leading to sepsis and even death,’ says Dr Christian Macutkiewicz, a consultant general and hepato-pancreatico-biliary surgeon at Manchester Royal Infirmary.

‘Seek urgent medical attention if you have sudden severe and constant pain in your stomach area with or without vomiting,’ adds Dr Kavvoura.

GALLSTONES

Any rapid weight loss can increase the risk of gallstone as the liver secretes more cholesterol into the bile, which can crystallise into gallstones.

A 2022 review in the Journal JAMA Internal Medicine found that using GLP-1s increased the risk of gallstones, particularly when used for longer durations (26 weeks or more) at higher doses (1mg or more of semaglutide once a week) and purely for weight loss.

PARALYSED GUT

Using GLP-1s increase the risk of paralysed gut and symptoms such as vomiting, nausea and pain, reported the journal Pharmaceuticals in 2024. The research showed that liraglutide (Victoza and Saxenda) had higher odds of gastroparesis than semaglutide. The condition is reversible once you stop taking the drug.

HAIR LOSS

‘While it’s not listed as a side-effect of weight-loss medications, I see an increasing number of people attending my clinic with hair shedding or thinning after using them,’ says Dr Wong.

This is possibly caused by the dramatic weight loss – once the weight is stabilised and your diet has the optimum nutrients – the hair shedding should gradually settle back to normal.

‘However, some experience hair loss without the extreme and rapid weight loss, suggesting there could be other mechanisms involved – such as a direct effect on hair follicle function,’ adds Dr Wong. ‘As an increasingly encountered problem, it’s an area that requires more research.’

DEPRESSION/SUICIDAL THOUGHTS

A study in Nature last year found there was 195 per cent higher risk of depression and a 106 per cent increased risk of suicidal behaviour in people taking GLP-1s – based on analysis of data from more than 162,000 people.

The Medicines and Healthcare products Regulatory Agency, the UK drugs watchdog, concluded that there is no causal link between these medications and depression.

However, Professor Le Roux explains that while the drug itself will assist with physical weight loss, there’s no evidence it will improve mood or how you feel about yourself, so people shouldn’t take it in the belief it will.

‘GLP-1s must be taken under medical supervision,’ he adds, ‘so their patient’s medical history can be assessed before taking the drug’.

‘OZEMPIC TEETH’

There are anecdotal reports of increasing numbers of people visiting their dentist with a range of oral side-effects including tooth decay, inflamed gums and dry mouth after using weight-loss jabs; it’s thought the drugs could lead to an environment such as dry mouth that speeds up decay.

Vomiting, another side-effect of the drugs, could erode the enamel, explains Mervyn Druian, a dentist at the London Centre for Cosmetic Dentistry.

WHAT HAPPENS WHEN YOU STOP TAKING THE JABS?

As with all diets, there comes a point where you stop losing weight – and you plateau. With weight-loss drugs, this usually occurs around 72 weeks of starting them, says Dr Kavvoura.

The body has achieved a new metabolic ‘set point’, explains Dr Mamta Joshi, an endocrinologist at Epsom and St Helier University Hospitals NHS Trust.

‘It’s at this point that people often come off the drugs, thinking they’ve lost the weight they need to and that drugs are no longer helping them lose more weight and thus are not necessary,’ explains Professor Le Roux.

‘However, the main problem with diets is that once people stop doing them, they tend to regain weight – and weight-loss drugs are no different.’

In an analysis of studies on both old and new GLP-1 medications earlier this year, researchers at the University of Oxford found that patients typically lost 8kg on weight-loss medication but returned to their original weight within ten months of stopping them.

There are some people who have dramatically changed their lifestyle through diet and exercise and manage to keep the weight off, but this is only around 2 to 5 per cent of people.

For everyone else, the weight-loss drugs are nothing more than brakes on the appetite centre and once they’ve been removed a decent amount of weight will return if alternative strategies are not put in place, says Dr Joshi.

SO WHY CAN’T I STAY ON THEM FOR EVER?

On the NHS, semaglutide (Wegovy) is prescribed for a maximum of two years only for weight loss; this is based on NICE recommendations and certainly due to cost implications, says Dr Joshi.

This two-year cap currently doesn’t apply to Mounjaro, but guidelines may change as data evolves. Privately, these drugs aren’t bound by these restrictions.

‘In coming years, if we are able to demonstrate no significant increase in risk of pancreatitis events and thyroid cancer then it’s likely we’ll be more relaxed about using GLP-1 drugs for longer periods,’ adds Dr Joshi.

CAN I MICRODOSE TO SAVE MONEY AND REDUCE SIDE-EFFECTS?

‘Microdosing’ – taking smaller doses of the medications than prescribed – has become increasingly popular, particularly in the US, where the cost of the new GLP-1 drugs is much higher than in the UK.

‘The main reason people do it is to save money, although some do it to lessen side-effects,’ says Professor Miras.

Others are also doing it to take that edge off hunger pangs and to lose smaller amounts, 5-10kg, of weight, too.

Essentially when you administer the jab you first attach the needle to a ‘pen’ cartridge containing the drug – you then turn the dose knob on the pen to obtain the dose amount (viewable in the dose counter window) – with microdosing you would turn the knob fewer times to administer 1mg instead of a standard starting dose of 2.5mg. Or you would inject less frequently than advised, so every two weeks instead of every week, explains Professor Miras.

However, using the drugs this way is off-label, meaning different from its intended use.

‘While it’s generally safe and already practised in some private clinics in the UK – there have been no clinical trials that have tried it in real patients,’ he adds.

‘Microdosing for reduced side-effects such as nausea does make some sense but shouldn’t be necessary on the lowest starting doses – and for losing weight, we know from the research that it’s dose dependent; the higher the dose the higher the weight loss with all the medications,’ says Professor Miras

‘It makes no sense to take lower doses because you will lose less weight. It is as simple as that.’

HOW ABOUT THE ‘GOLDEN DOSE’?

After the four weekly doses a pen contains are used up, there is likely to be some liquid left. Some influencers have taken to calling this a fifth dose or the ‘golden dose’. But doctors warn against treating it like a bonus jab as it is at best potentially ineffective – at worst unsafe. The overfill is deliberate to ensure four full doses, but the extra is not clinically recommended as medication.

P.S. EVEN BETTER JABS – OR A DAILY PILL – ARE JUST AROUND THE CORNER

The next generation of weight-loss drugs look to deliver even more weight loss in safer ways – and with longer-lasting effects, says Professor Le Roux.

The newest drug on the block is likely to be CagriSema, and then retatrutide.

But the next big blockbuster could be MariTide, developed by Amgen, a once monthly jab (rather than weekly).

Like Mounjaro, MariTide targets the hormone receptors GLP-1, but unlike Mounjaro it blocks GIP.

Results of a trial published in June in the New England Journal of Medicine showed people lost up to 20 per cent weight loss in 52 weeks; significantly, many participants maintained the weight loss for six months after stopping taking it (with semaglutide, studies show patients regain an average two thirds of their weight loss within just 12 months). It could be available in 2028.

Another option coming soon could be weight-loss pills targeting the same hormones.

As Professor Miras explains: ‘Oral formulations are generally more acceptable by patients even if taken daily.’ These are also expected to be cheaper, although the results aren’t quite as impressive as the jab.

Orgorglipron, a daily pill that works like semaglutide, has just been shown to help participants lose 20 per cent of more of their body weight over 72 weeks, reported the New England Journal of Medicine. It’s expected to become available in the UK in 2026.