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
Free tracker included with every download this week
Does GLP-1 work for weight loss in the UK?
Yes, GLP-1 medications can help with weight loss. Clinical trials show that prescription GLP-1 weight loss injections help adults lose an average of 14–21% of their body weight when combined with lifestyle changes. These medications work by reducing appetite and helping you feel fuller after eating. In the UK, weight management medications like Mounjaro and Wegovy are available through NHS specialist services or private prescribing. Whether GLP-1 is right for you depends on your individual health, BMI, and eligibility criteria set by your GP or prescriber.
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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 GLP-1 medications for weight management
Three prescription GLP-1 medications are currently licensed in the UK for weight management: Mounjaro (tirzepatide), a dual GIP and GLP-1 receptor agonist given once weekly; Wegovy (semaglutide), a GLP-1 receptor agonist also given once weekly; and Saxenda (liraglutide), a daily GLP-1 injection. In the SURMOUNT-1 clinical trial, adults on Mounjaro 15 mg lost an average of 20.9% of their body weight over 72 weeks. In the STEP-1 trial, Wegovy achieved approximately 14.9% average weight loss at 68 weeks. These results are typical averages — individual weight loss varies significantly. All three medications are prescription-only and require a clinical assessment. They work alongside a reduced-calorie diet and increased physical activity, not as replacements for lifestyle changes.
- Eligibility: Adults with a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, high blood pressure, or heart disease
- Dose escalation: Doses are increased gradually over weeks to minimise side effects and allow your body to adjust
- Side effects: Common effects include nausea, diarrhoea, and constipation, which often improve as your body adjusts
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
How to access GLP-1 medications in the UK
Access to GLP-1 weight loss medication in the UK follows two main routes. The NHS route involves referral from your GP to a tier 3 specialist weight management service, where a multidisciplinary team assesses your health and prescribes medication if appropriate. NHS access is free, but waiting lists can be several months or longer depending on your area. The private route involves an online consultation with a UK-licensed prescriber through a GPhC-registered pharmacy — you can access this without an NHS referral. Private prescriptions typically cost £129–£320 per month depending on dose. Try our free GLP-1 weight loss calculator above to explore projected outcomes at different doses. Your GP can discuss which route and medication is most suitable for your individual circumstances, taking into account your health history and weight loss goals.
- 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.
How long does it take for GLP-1 to work for weight loss?
Weight loss typically begins within the first 4 weeks, with the most significant changes seen between weeks 8–16 as your dose increases. Full benefits are usually apparent at 12–16 weeks once you've reached your target dose. Results continue to improve over several months of treatment.
Can I use GLP-1 medication without changing my diet?
No. GLP-1 medications work best when combined with a reduced-calorie diet and increased physical activity. The medication supports these changes by reducing appetite and cravings, but dietary and exercise modifications are essential for sustained weight loss.
Will I regain weight when I stop GLP-1?
Weight regain is possible after stopping GLP-1, particularly if lifestyle changes are not maintained. Your GP or prescriber can discuss long-term treatment planning. Some people continue on medication long-term, whilst others use it as a bridge to establish new eating habits.
How do I know if I'm eligible for GLP-1 weight loss medication in the UK?
You may be eligible if you have a BMI of 30 or above, or 27 or above with a weight-related health condition. The best way to find out is to speak to your GP, who can assess your individual health and discuss whether medication is appropriate for you.
What's the difference between Mounjaro and Wegovy for weight loss?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist that achieved 20.9% average weight loss in trials. Wegovy (semaglutide) is a GLP-1 agonist alone with approximately 14.9% average weight loss. Both are effective; your prescriber will recommend based on your health profile and individual needs.
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.