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?
If you're looking for weight management medication in the UK, you've likely heard about GLP-1 injections. Three prescription options are currently licensed for weight loss: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Each works differently and suits different people. This guide explains how they compare, who's eligible, and how to access them through the NHS or privately. Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses.
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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 Options for Weight Loss
Mounjaro (tirzepatide) is a once-weekly injection that activates two hormone pathways (GIP and GLP-1). In clinical trials, it helped adults lose an average of 15–21% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is also once-weekly and activates the GLP-1 pathway only. Clinical trials showed average weight loss of around 15% of body weight at 68 weeks on the maximum dose of 2.4mg.
Saxenda (liraglutide) is a daily injection (not weekly) with a maximum dose of 3mg. It's been available longer than the other two and showed average weight loss of 5–10% of body weight in trials.
Individual results vary significantly. All three are prescription-only and require a clinical assessment before being prescribed. Your GP or a licensed prescriber will assess which, if any, is suitable for your health profile and weight management goals.
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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.
NHS vs Private Access — How to Get Started
NHS access: Weight loss injections are available through NHS specialist tier 3/4 weight management services. You'll need a referral from your GP. Availability and waiting times vary significantly by region—some areas have waiting lists of many months.
Private access: You can be prescribed GLP-1 medication through private online clinics without an NHS referral. A UK-licensed prescriber assesses your eligibility online, and if suitable, issues a prescription dispensed by a registered pharmacy.
Next step: Start by speaking with your GP about your weight management goals. Check your BMI using our free BMI calculator—eligibility typically requires a BMI of 30 or above, or 27+ with weight-related health conditions like type 2 diabetes or high blood pressure. Your GP can discuss available options and timelines.
- 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?
Mounjaro (tirzepatide) activates two hormone pathways (GIP and GLP-1), while Wegovy (semaglutide) activates GLP-1 only. In clinical trials, Mounjaro showed slightly higher average weight loss (15–21% vs 15%), but both are effective. Individual response varies. Your prescriber will assess which suits you best based on your health profile and any other medications.
How long does it take to see weight loss results with GLP-1 medication?
Weight loss typically begins within the first 2–4 weeks, though it can take longer for some people. Most people see noticeable changes within 8–12 weeks as their dose increases. Results depend on dose, diet, physical activity, and individual factors. Track your progress with our free progress tracker to monitor changes over time.
Am I eligible for GLP-1 weight loss medication on the NHS?
NHS weight loss injections are available through specialist services for adults with a BMI of 30 or above, or 27+ with weight-related health conditions (type 2 diabetes, high blood pressure, sleep apnoea). Access varies by region and waiting times can be long. Ask your GP about your local tier 3 weight management service and eligibility.
Can I switch between Mounjaro and Wegovy?
Any switch between GLP-1 medications must be managed by your prescriber. While approximate dose equivalences exist (Mounjaro 5mg ≈ Wegovy 0.5mg), there's no official conversion chart. Your prescriber will guide you through any transition and monitor your response carefully.
What happens if I want to stop GLP-1 weight loss medication?
You can stop GLP-1 medication at any time, but discuss this with your prescriber first. Weight regain can occur after stopping, typically over several months. Many people return to lifestyle support, dietary changes, and our free progress tracker to maintain weight loss achieved during treatment.
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.