Everything you need to know about weightloss drugs
Nobody knows more about how many people struggle with their weight than a GP; most of the patients I see have been trying to lose weight for years, sometimes shifting some of
the excess but rarely keeping it off. Throughout my career, options for treatment have been limited. So, overall, I’m delighted we finally have medication options – the GLP-1 drugs – that can help to deliver really meaningful weight loss, and I’m inundated with patients who want to try them. But as a GP, I can’t (yet) prescribe them on the NHS. What’s more, they’re not a magic bullet and there are precautions to take.
What are GLP-1s?
The GLP-1 (officially, GLP-1 agonist) drugs mimic the action of a naturally produced hormone, glucagon-like peptide-1. They act on your body in a number of ways – triggering insulin release from your pancreas; blocking a hormone called glucagon, which raises blood glucose; slowing stomach emptying after eating, so you feel more full; and affecting the hunger and fullness centres of your brain.
First developed to control blood glucose in people with type 2 diabetes, the ‘side-effect’ of weight loss seen in many patients was rapidly seized upon. Liraglutide became the first GLP-1 to be licensed for weight loss in this group in 2014, with the brand name Saxenda. Since then, several others have been approved and more are going through trials.
What is the best injection for weight loss?
Just as different antibiotics and blood pressure drugs in the same class have different effects, the weight loss seen with GLP-1s varies. On average, on treatment, people on liraglutide lost up to 6% of their body weight after 26 weeks; on semaglutide (brand name Wegovy) 14% after 68 weeks; and on tirzepatide (Mounjaro) 18% after 72 weeks. Mounjaro contains two ingredients, mimicking the effect of both GLP-1 and another gut hormone, GIP. Retatrutide isn’t yet licensed but works on the same two hormones as well as glucagon receptors – in studies, it led to weight loss of 22% after 48 weeks.
Can my GP prescribe weight loss injections?
Access on the NHS depends on BMI (body mass index – over 30 is the obese category and over 40 severe obesity) and whether you have ‘comorbidities’ – medical conditions such as high blood pressure, heart disease, obstructive sleep apnoea etc. These also determine whether you can be referred to an NHS specialist weight management service.
Although NICE guidance limits NHS availability to patients already under specialist services, in 2025, the plan is to announce other groups who may be eligible in the next three years. NICE estimates about 220,000 people – out of 3.4m people with a BMI over 35 and at least one weight-related illness – will be able to access the drugs by 2028.
Can I buy GLP-1s privately?
Many private providers of GLP-1s have sprung up. As a prescription drug, GLP-1s should only be given after a full assessment from a qualified prescriber to make sure you meet the licensed weight criteria – including a BMI over 30, or over 27 if you have a weight-related condition.
Regulations have been tightened up and online pharmacies will now have to employ stricter checks to prevent people who are already a healthy weight or have a history of eating disorders from buying weight-loss jabs.
What dose will I need?
Both Wegovy and Mounjaro come in several doses. You start with the lowest – a once-weekly injection – to minimise side-effects. After four weeks, you move to the lowest ‘maintenance dose’. After that, you and your healthcare professional decide between you whether and how fast/far to increase the dose, waiting at least four weeks before the next increase. This depends on whether (and how much) you’re losing weight and any side-effects. If you’re losing weight steadily, it may make sense to stay on that dose: losing weight too fast puts you at higher risk of muscle loss and vitamin/mineral deficiency.
What are the side effects of weight loss jabs?
In clinical trials, many patients taking GLP-1s had to stop the drugs because they couldn’t tolerate the side-effects – including nausea (the most common), vomiting, constipation, dehydration and gallstones. Many of these side-effects happen because the drugs are acting as they’re designed – slowing stomach emptying so you feel full for longer. They tend to be worse when you first start a new dose, and usually settle within weeks. But there are lots of steps you can take:
Reset your portion size. A side-plate-sized meal is a good place to start.
Fatty or spicy foods are best avoided
if you’re having side-effects.Eat slowly, pausing to check how
full you feel.Make sure you drink plenty of clear (non-alcoholic) fluids.
Don’t exercise too vigorously
after eating.Don’t move to a higher dose until
your symptoms are under control.
What do I eat when I’m on GLP-1s?
With food intake reduced by up to 40% on GLP-1s, make sure you’re getting enough healthy nutrients to avoid the risk of malnutrition. This includes fluids as well as vitamins, minerals, protein and healthy fats. It’s also key to get enough fibre – avoid processed foods and stick to unrefined (wholegrain, wholemeal etc) carbs, along with plenty of fruit and veg.
One of the other downsides of GLP-1s is that it’s not just fat you’ll be losing – up to 40% of the weight loss seen with GLP-1 use is muscle. Planning every meal around a high-quality source of protein will help. So, too, will regular exercise – including resistance training, which encourages muscle regeneration.
How long do weight loss injections last?
This is the difficult bit. In one study, people regained 67% of the weight they had lost a year after stopping Wegovy. Tapering your dose to come off slowly, plus diet and exercise, could reduce that risk. But we may need to accept that, as with other chronic diseases, for some, lifelong treatment is the only answer.
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