GLP-1 Weight Loss Injections UK: How They Work, Costs & Where to Buy

GLP-1 (glucagon-like peptide-1) is a hormone naturally produced in your gut after eating. It plays a crucial role in regulating appetite, blood sugar levels, and digestion. GLP-1 receptor agonists are medications that mimic the effects of this hormone, but at much higher and more sustained levels than your body produces naturally. These medications were originally developed for managing type 2 diabetes, where they help control blood sugar by stimulating insulin production and reducing glucagon secretion. Researchers discovered that patients taking GLP-1 medications also experienced significant weight loss as a side effect, which led to the development of higher-dose formulations specifically approved for weight management. GLP-1 receptor agonists work through three main mechanisms: they slow gastric emptying so food stays in your stomach longer and you feel full for longer after meals; they reduce appetite signals in the hypothalamus (the brain's hunger centre); and they improve insulin sensitivity, which helps your body process food more efficiently. The combined effect is a meaningful reduction in calorie intake without the constant hunger that typically accompanies dieting.

Four GLP-1 medications are commonly discussed in the UK, though not all are approved for weight management:

• Mounjaro (tirzepatide) is technically a dual GIP/GLP-1 receptor agonist, meaning it activates both the GLP-1 and GIP (glucose-dependent insulinotropic polypeptide) receptors. This dual action may explain why it produces greater weight loss than GLP-1-only medications. Made by Eli Lilly, injected weekly, available in six doses from 2.5mg to 15mg. Clinical trials showed up to 22.5% body weight loss.
• Wegovy (semaglutide 2.4mg) is a GLP-1 receptor agonist approved specifically for weight management. Made by Novo Nordisk, injected weekly. It is the same active ingredient as Ozempic but at a higher dose. Clinical trials showed approximately 15% body weight loss.
• Saxenda (liraglutide 3mg) is an older GLP-1 receptor agonist. Made by Novo Nordisk, injected daily. Less effective than newer options but has the longest safety track record. Approximately 8% body weight loss in trials.
• Ozempic (semaglutide 1mg) is approved for type 2 diabetes only, not weight management. Some prescribers prescribe it off-label for weight loss. It is the same molecule as Wegovy but at a lower dose.

For a detailed comparison of the two most popular options, see our Mounjaro vs Wegovy guide. For a comparison including Ozempic, see our Mounjaro vs Ozempic comparison.

GLP-1 injections are available both privately and through the NHS, though NHS access remains limited. Private prices (per month):

• Mounjaro: £130-320 depending on dose. The 2.5mg starter dose is cheapest. Prices vary by up to £100 between pharmacies for the same dose.
• Wegovy: £149-299 depending on dose and availability.
• Saxenda: £100-200. Cheapest per month but least effective.

NHS: Free if you are referred through a specialist weight management service and meet the eligibility criteria. However, waiting lists can be long and access varies by region. Check our NHS eligibility checker to see if you might qualify. The biggest savings opportunity for Mounjaro is comparing pharmacy prices. Differences of £50-100 per month between pharmacies are common. Our price comparison table tracks live prices from 60+ UK pharmacies. Use our cost calculator to estimate your total treatment cost.

GLP-1 receptor agonists share a similar side effect profile because they work through the same mechanism. The most common side effects are gastrointestinal:

• Nausea affects 15-25% of users. Usually worst during the first 1-2 weeks after starting or increasing dose, then improves. See our nausea management tips.
• Diarrhoea affects 10-17% of users. Usually temporary.
• Constipation affects 6-12% of users. Staying hydrated helps.
• Reduced appetite is technically the intended effect but can feel like a side effect if very pronounced.
• Injection site reactions are usually mild and short-lived.

Serious but rare side effects include pancreatitis (inflammation of the pancreas) and gallbladder problems. GLP-1 medications should not be used by people with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2 (MEN2). Most side effects are temporary and manageable with dose titration, dietary adjustments, and time. For comprehensive information, see our complete side effects guide.

The fastest route to GLP-1 injections in the UK is through a private online pharmacy. The process is straightforward:

• Step 1: Choose a GPhC-registered pharmacy from our comparison page.
• Step 2: Complete an online consultation (typically 5-10 minutes) providing your medical history, current medications, height, weight, and health conditions.
• Step 3: A qualified prescriber reviews your information and, if appropriate, issues a prescription.
• Step 4: Your medication is dispatched in temperature-controlled packaging, usually arriving within 1-3 working days.

To be eligible, you generally need a BMI of 30+ (or 27+ with weight-related health conditions). For the full step-by-step process, see our guide to getting Mounjaro. To find the cheapest Mounjaro prices, visit our price comparison page or read our cheapest Mounjaro guide for savings tips.