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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Weight Loss Medication in the UK: Your Complete Guide
If you're exploring weight management options in the UK, prescription medication may be part of your journey. The NHS and private prescribers now offer several evidence-based weight loss injections for eligible adults. This guide covers the prescription weight loss medications available, who can access them, how they work, and the difference between NHS and private routes. Whether you're starting your weight loss journey or looking for additional support, understanding your medication options is an important first step.
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Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
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.
UK-Licensed Weight Loss Medications and How They Work
Three prescription weight management medications are currently licensed in the UK for adults with obesity or overweight with health complications. Mounjaro (tirzepatide) is a once-weekly injection that acts as a dual GIP and GLP-1 receptor agonist, potentially helping to reduce appetite and support weight loss. Clinical trials showed participants using Mounjaro lost an average of 15–21% of their body weight over 72 weeks, though individual results vary significantly.
Wegovy (semaglutide) is a once-weekly GLP-1 injection licensed specifically for weight management. In the STEP-1 clinical trial, participants lost an average of approximately 15% of their body weight over 68 weeks when combined with a reduced-calorie diet and increased physical activity.
Saxenda (liraglutide) is a daily GLP-1 injection and was the first weight loss injection licensed in the UK, though less commonly prescribed today than Mounjaro or Wegovy.
All three are prescription-only medicines requiring clinical assessment before being prescribed. Use our free GLP-1 weight loss calculator above to explore projected outcomes at different doses.
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Eligibility and How to Access Weight Loss Treatment
To be eligible for prescription weight loss medication in the UK, you typically need a BMI of 30 kg/m² or above, or a BMI of 27–29.9 kg/m² if you have a weight-related health condition such as type 2 diabetes, high blood pressure, sleep apnoea, or cardiovascular disease. Use our free BMI calculator above to check your personal BMI instantly.
NHS access: Referral through your GP to a tier 3 specialist weight management service. Availability varies by region and waiting lists can be lengthy.
Private access: Online consultation with a UK-licensed prescriber, available without NHS referral. Your GP can discuss both routes with you, and a prescriber will assess whether medication is clinically appropriate for your individual circumstances. Weight loss medication works best alongside dietary changes and increased physical activity.
- 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's the difference between Mounjaro and Wegovy for weight loss?
Both are once-weekly injections licensed for weight management in the UK. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1-only agonist. Clinical trial data shows both support meaningful weight loss when combined with lifestyle changes. Results vary between individuals. A prescriber can advise which may be more suitable for you.
How do I know if I'm eligible for weight loss medication in the UK?
You may be eligible if you have a BMI of 30 or above, or 27 or above with weight-related health conditions like diabetes or high blood pressure. Ethnicity affects eligibility thresholds — South Asian, Chinese, Black African, and Black Caribbean adults have lower thresholds due to higher health risks. Your GP or a licensed prescriber can assess your individual eligibility.
What's the difference between NHS and private weight loss medication access?
NHS access requires a GP referral to specialist tier 3 services; availability varies by region and waiting lists can be long. Private access is through online consultation with a UK-licensed prescriber without NHS referral, and medication is available more quickly. Both routes require clinical assessment. Costs, timelines, and availability differ — discuss both options with your GP.
How much weight can I expect to lose on weight loss medication?
Clinical trials show average weight loss of 15–21% of body weight, but individual results vary significantly. Weight loss depends on the specific medication, dose, how long you take it, and how well you combine it with dietary changes and physical activity. A prescriber can discuss realistic expectations based on your personal circumstances.
Are weight loss injections safe?
Prescription weight loss medications are licensed and have undergone safety testing. Common side effects include nausea, diarrhoea, and constipation, which often improve over time. Serious side effects are rare but can include pancreatitis and gallbladder problems. A prescriber will assess whether the medication is safe for you based on your medical history and current health.
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.