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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How to Order Mounjaro vs Wegovy in the UK
If you're considering weight management injections in the UK, you may be wondering whether to order Mounjaro (tirzepatide) or Wegovy (semaglutide). Both are prescription-only GLP-1-based medications licensed for weight loss, but they work differently and have different ordering processes. This guide compares both options to help you understand the differences when discussing them with your GP or a licensed prescriber.
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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.
Key Differences Between Mounjaro and Wegovy
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two separate hormone pathways in the body. Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single pathway. In the SURMOUNT-1 clinical trial, Mounjaro at 15 mg showed average weight loss of approximately 20.9% body weight over 72 weeks, whilst Wegovy in the STEP-1 trial demonstrated average weight loss of 14.9% at 68 weeks on the maximum 2.4 mg dose. Both results were achieved alongside reduced-calorie diet and increased physical activity, and individual outcomes vary significantly.
- Mounjaro dose range: 2.5 mg to 15 mg once weekly
- Wegovy dose range: 0.25 mg to 2.4 mg, with the first four doses at lower escalation levels
- Both require minimum 4 weeks at each dose before increasing
- Starting doses differ: Mounjaro starts at 2.5 mg; Wegovy starts at 0.25 mg
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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.
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Ordering and Eligibility — What You Need to Know
Both Mounjaro and Wegovy are prescription-only medicines in the UK requiring a clinical assessment before ordering. You must have a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with at least one weight-related health condition such as type 2 diabetes, high blood pressure, or cardiovascular disease. Eligibility thresholds may be lower for adults of South Asian, Chinese, Black African, or Black Caribbean heritage.
To order either medication, you can be referred to an NHS specialist weight management service through your GP, or use a GPhC-registered online prescribing service for private access. NHS access varies by region and may involve waiting lists. Our GLP-1 weight loss calculator can help you understand potential outcomes, and our BMI calculator shows whether you fall within eligible ranges based on your height and current weight.
- 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.
Can I switch from Mounjaro to Wegovy?
Yes, you can switch between medications, but this must be managed by your prescriber. There is no official conversion chart — approximate equivalence suggests Mounjaro 15 mg is similar to Wegovy 2.4 mg, but dosing adjustments are individualised. A prescriber will assess your response and any side effects to determine the best transition plan.
Which is more effective — Mounjaro or Wegovy?
Clinical trials showed Mounjaro achieved slightly higher average weight loss than Wegovy, but results vary widely between individuals. What works best depends on your personal health profile, how you respond to the medication, and side effects you may experience. Your prescriber will help determine which is most suitable for you based on your health history.
How do I order Mounjaro or Wegovy privately in the UK?
Contact a GPhC-registered online prescribing service. You'll complete an online clinical assessment with a UK-licensed prescriber. If approved, a prescription is issued and the medication is dispensed by a registered pharmacy. This route doesn't require NHS referral but involves costs ranging from approximately £129–£320 monthly depending on dose and provider.
Are both medications available on the NHS?
NICE has approved both tirzepatide (Mounjaro) and semaglutide (Wegovy) for NHS use through specialist tier 3 weight management services. However, availability varies significantly by region and ICB. Access typically requires referral from your GP and can involve substantial waiting lists.
What are the main side effects of each medication?
Both commonly cause nausea, diarrhoea, vomiting, and constipation, especially during dose escalation. Mounjaro and Wegovy have similar side effect profiles. Most side effects improve over time as your body adjusts. Always report any concerning or persistent symptoms to your prescriber — they can advise on managing effects or adjusting your 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.