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?
There's no single "best" GLP-1 for weight loss — the right medication depends on your individual health, preferences, and how your body responds. Three GLP-1 medications are currently licensed for weight management in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Each works slightly differently and produces different average results in clinical trials. Your GP or a licensed prescriber will assess which option suits you best based on your medical history, BMI, and weight-related health conditions. This guide compares the main options to help you understand what's available.
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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.
GLP-1 Medications Approved for UK Weight Management
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — meaning it activates two hormone pathways rather than one. In clinical trials (SURMOUNT-1), participants on the maximum 15 mg dose lost an average of 20.9% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity. Mounjaro is given as a once-weekly injection, starting at 2.5 mg and escalating gradually to a maximum of 15 mg.
Wegovy (semaglutide) is a GLP-1-only receptor agonist. In the STEP-1 clinical trial, participants on the maximum 2.4 mg dose lost approximately 14.9% of their body weight over 68 weeks. Wegovy is also a once-weekly injection, starting at 0.25 mg and escalating over 16 weeks to 2.4 mg. Because Wegovy and Mounjaro have different mechanisms, clinical trial results differ — though individual results vary considerably.
Saxenda (liraglutide) is a daily GLP-1 injection (not once-weekly). Average weight loss is typically less than Mounjaro or Wegovy, but some people prefer a different mechanism or injection schedule. Maximum dose is 3 mg daily.
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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.
Choosing the Right GLP-1 for Your Situation
The "best" GLP-1 for weight loss is the one that your prescriber determines is most suitable for your individual health profile. Consider these factors: mechanism of action — Mounjaro's dual mechanism produces higher average weight loss in trials, but Wegovy may suit others equally well; injection frequency — Mounjaro and Wegovy are once-weekly (easier to remember), while Saxenda is daily; side effect profile — nausea and gastrointestinal effects are common with all three, but severity varies; cost — if accessing privately, prices vary by medication and dose; NHS availability — your local weight management service may have formulary restrictions, so not all options may be available to you.
Use our GLP-1 weight loss calculator to explore potential outcomes at different doses, and our free BMI calculator to understand your current weight category. Your prescriber will discuss which option is most appropriate after a clinical assessment.
- 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 better than Wegovy for weight loss?
In clinical trials, Mounjaro showed higher average weight loss (up to 20.9%) compared to Wegovy (14.9%) — but this reflects trial averages. Individual results vary significantly. Mounjaro's dual GIP/GLP-1 mechanism differs from Wegovy's single GLP-1 mechanism, which may explain the difference. Your prescriber will assess which suits your health profile best.
Can I switch between GLP-1 medications?
Potentially, yes — but only under prescriber guidance. There's no official conversion chart between medications. If one medication isn't suitable or effective, your prescriber may recommend switching to an alternative. Never stop or switch without medical advice, as this affects your dosing schedule.
What's the difference between Wegovy and Ozempic?
Both contain semaglutide, but Ozempic is approved for type 2 diabetes (doses up to 2 mg) and is not licensed for weight loss in the UK. Wegovy is the licensed weight management version (doses up to 2.4 mg). Using Ozempic off-label for weight loss is not recommended — Wegovy is the appropriate licensed option.
How long does it take to see results with GLP-1 medication?
Most people notice appetite reduction and early weight loss within 2–4 weeks of starting, particularly when the dose increases. Significant weight loss typically becomes apparent after 8–12 weeks. Clinical trial data comes from 68–72 weeks of treatment, so longer-term use produces better results than short-term use.
Can I access GLP-1 weight loss medication on the NHS?
Yes, through specialist tier 3 weight management services — ask your GP for a referral. However, NHS availability varies significantly by region and waiting times can be long. Private online prescribing is also available; you'll need a clinical assessment from a UK-licensed prescriber and prescription from a GPhC-registered pharmacy.
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.