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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What Are Mounjaro Substitutes? UK Alternatives Explained
If you're considering Mounjaro or looking for an alternative, the main substitute available in the UK is Wegovy (semaglutide). Both are prescription-only weight loss injections, but they work slightly differently and may have different availability depending on whether you're accessing treatment through the NHS or privately. Understanding the options helps you and your GP or prescriber find the right approach for your health needs.
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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.
Wegovy — The Main Mounjaro Alternative in the UK
Wegovy (semaglutide) is the primary alternative to Mounjaro available in the UK. Like Mounjaro, it's a once-weekly injectable medication licensed for weight management in adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions. The key difference is the mechanism: Wegovy is a GLP-1 receptor agonist, activating one hormone pathway, whereas Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist.
In clinical trials (STEP-1), Wegovy helped participants lose an average of approximately 14.9% of their body weight at the maximum dose of 2.4 mg — though individual results vary significantly. Wegovy starts at 0.25 mg and escalates over 16 weeks to the maintenance dose. Both medications are available privately through online prescribing or via NHS specialist weight management services, though NHS access varies by region and waiting lists can be lengthy. Your GP or a licensed prescriber can assess which option suits your circumstances and health profile.
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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.
Other GLP-1 Weight Loss Options and Clarifications
Saxenda (liraglutide) is another GLP-1 medication licensed in the UK for weight management, though it's a once-daily injection rather than weekly. Ozempic is often confused with Wegovy — both contain semaglutide, but Ozempic is approved only for type 2 diabetes (up to 2 mg) and using it for weight loss is off-label. Wegovy is the licensed weight management version at 2.4 mg.
Access to these medications differs: NHS specialist services typically assess all options, while private routes may have wider availability. Tirzepatide (Mounjaro) and semaglutide (Wegovy) are the two most commonly prescribed choices currently. Use our GLP-1 weight loss calculator to understand potential outcomes at different doses, and our BMI calculator to assess your starting point and eligibility for treatment.
- 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 Wegovy a direct substitute for Mounjaro?
Wegovy is the closest UK alternative to Mounjaro. Both are once-weekly injections for weight management. Wegovy uses a single GLP-1 mechanism, while Mounjaro uses dual GIP+GLP-1. Clinical trial data shows both are effective, though results vary individually. A prescriber can advise which is more suitable for you.
Can I switch from Mounjaro to Wegovy?
Yes, switching is possible but must be managed by your prescriber. There's no official conversion chart between doses, though approximate equivalences exist. Stopping one and starting another requires clinical guidance to minimise side effects and maintain consistency.
What's the difference between Ozempic and Wegovy?
Both contain semaglutide, but Ozempic is licensed for type 2 diabetes (up to 2 mg) and using it for weight loss is off-label. Wegovy is the licensed weight management version at 2.4 mg. In the UK, Wegovy is the appropriate prescription for weight loss.
How do I access Mounjaro alternatives on the NHS?
Referral to a tier 3 specialist weight management service is typically required. Your GP can refer you if you meet eligibility criteria (BMI 30+ or 27+ with health conditions). NHS availability and waiting times vary significantly by region and ICB.
Are Mounjaro alternatives available privately?
Yes. Wegovy, semaglutide, and other GLP-1 medications are available privately through online prescribing services following a clinical assessment. This route typically has faster access than NHS services but involves private costs, ranging from approximately £129–£320 per month depending on dose.
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.