The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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Different Weight Loss Injections Available in the UK
Several prescription weight loss injections are now available in the UK, offering different approaches to weight management. These include GLP-1 receptor agonists like Wegovy and Saxenda, and the dual GIP/GLP-1 medication Mounjaro. Each works differently and has distinct eligibility criteria. Understanding your options helps you have an informed conversation with your GP or prescriber about which might suit your situation. This guide covers the main weight loss injections licensed for use in the UK and how they compare.
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What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
The Main Weight Loss Injections Licensed in the UK
Three prescription weight loss injections are currently licensed for weight management in the UK:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist administered once weekly. Clinical trials showed an average weight loss of 15–21% of body weight, though individual results vary significantly.
- Wegovy (semaglutide) — a GLP-1 receptor agonist given once weekly. The STEP trial demonstrated approximately 15% average weight loss alongside reduced-calorie diet and increased physical activity.
- Saxenda (liraglutide) — a GLP-1 receptor agonist administered daily by injection (not weekly like Mounjaro or Wegovy). Approved for weight management in adults with a BMI of 30 or above, or 27 or above with weight-related conditions.
All three are prescription-only medicines requiring clinical assessment before being prescribed. They work by activating natural hormone pathways that help regulate appetite and food intake.
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
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How to Access Weight Loss Injections in the UK
Weight loss injections in the UK are available through two main routes. NHS access is via referral to specialist tier 3 or tier 4 weight management services, though regional availability and waiting times vary considerably. Private access is through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber. Both routes require eligibility assessment based on BMI and health factors. Use our free GLP-1 weight loss calculator to explore potential outcomes, and our BMI calculator to check your current category. Your GP can advise which route and medication might be most suitable for your circumstances.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
What is the difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy is a GLP-1 agonist only. Mounjaro showed average weight loss of 15–21% in trials versus approximately 15% for Wegovy. Both are once-weekly injections. The choice depends on individual health factors and prescriber assessment. Results vary between individuals.
Is Ozempic the same as Wegovy?
Both contain semaglutide, but Ozempic is licensed for type 2 diabetes (doses up to 2mg) while Wegovy is specifically licensed for weight management (up to 2.4mg). Ozempic is not licensed for weight loss in the UK, so Wegovy is the appropriate weight management option.
Can I get weight loss injections on the NHS?
Yes, through specialist weight management services (tier 3/4). You'll need a GP referral and assessment. However, NHS availability varies significantly by region and waiting times can be lengthy. Private access through online prescribers offers faster availability but involves private costs.
What are the main side effects of weight loss injections?
Common side effects include nausea, diarrhoea, constipation, and stomach pain—these often improve over time. Serious side effects are rare but can include pancreatitis or gallbladder issues. Always discuss potential side effects with your prescriber before starting treatment.
How much weight will I lose with these injections?
Average weight loss from clinical trials is 15–21% of body weight, but individual results vary considerably. Weight loss depends on dose, adherence, dietary changes, and physical activity. Your prescriber can discuss realistic expectations based on your personal circumstances.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.