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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Which GLP-1 Is Best for Weight Loss in the UK?
There are three prescription GLP-1 medications licensed for weight management in the UK: Mounjaro, Wegovy, and Saxenda. Which one is "best" depends on your individual health, eligibility, and circumstances — not a one-size-fits-all answer. This guide compares the three options, explains how they work differently, and helps you understand which might be suitable for you based on NHS eligibility criteria and what's available through your GP or private prescription pathways.
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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
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — the newest option in the UK. It works by activating two hormone pathways, potentially offering stronger appetite suppression. Clinical trials showed average weight loss of 15–21% of body weight. Maximum dose is 15 mg once weekly. Wegovy (semaglutide) activates only the GLP-1 pathway and has more established long-term data in the UK market. Average weight loss at the maximum 2.4 mg dose is approximately 15% of body weight. Saxenda (liraglutide) is an older GLP-1 injection requiring daily administration (not weekly), with a maximum dose of 3 mg daily. Average weight loss is approximately 5–10% of body weight.
- Mounjaro: Once weekly, dual mechanism, higher average weight loss in trials
- Wegovy: Once weekly, established safety profile, strong clinical evidence
- Saxenda: Once daily, longer history in the market, lower average weight loss
Important: Individual results vary significantly. All are prescription-only medicines requiring clinical assessment before prescription.
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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 in the UK
You may be eligible for prescription weight loss medication if you have a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Use our free BMI calculator above to check your personal BMI. Lower thresholds apply if you're of South Asian, Chinese, Black African, or Black Caribbean heritage. NHS access is through specialist tier 3 weight management services — your GP can refer you, though waiting lists vary by region. Private access is available through licensed prescribers following an online consultation. A prescriber will assess which medication suits your health profile, as eligibility and suitability differ between individuals. Your GP is the best starting point to discuss weight loss options.
- 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.
Is Mounjaro or Wegovy better for weight loss?
Mounjaro showed slightly higher average weight loss (15–21%) than Wegovy (15%) in clinical trials, but results vary significantly between individuals. "Better" depends on your health, other medications, and what your prescriber recommends. Neither is universally superior — they work differently and suit different people.
Can I get GLP-1 medication on the NHS in the UK?
Yes. NICE has approved tirzepatide (Mounjaro) for NHS specialist weight management services. Access is through referral to tier 3 services, though regional availability and waiting times vary widely. Your GP can refer you if you meet eligibility criteria.
What is the difference between Mounjaro and Wegovy?
Mounjaro activates two hormone pathways (GIP and GLP-1), while Wegovy activates only GLP-1. Mounjaro is injected once weekly, starting at 2.5 mg and increasing to a maximum of 15 mg. Wegovy is also weekly, ranging from 0.25 mg to 2.4 mg. Clinical evidence suggests Mounjaro may produce slightly higher average weight loss.
How do I know which GLP-1 medication I'm eligible for?
Eligibility is assessed individually by a prescriber based on your BMI, weight-related health conditions, other medications, and medical history. Your GP can discuss your options, or you can have a private online consultation with a licensed UK prescriber. Both will determine which medication is appropriate for you.
Do GLP-1 injections work for everyone?
No. Clinical trials show these medications help many people lose weight, but results vary. Some people lose more weight than others, and some may not respond significantly. They work best alongside a reduced-calorie diet and increased physical activity. A prescriber will monitor your progress and adjust treatment if needed.
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.