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- 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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Mounjaro vs Wegovy: Which Weight Loss Injection Can You Buy in the UK?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections available in the UK, but they work differently and may suit different people. This guide compares their mechanisms, clinical trial results, doses, and how to access each one. Both require a clinical assessment and prescription from a UK-licensed prescriber before you can buy either medication. Understanding the differences can help you discuss options with your GP or 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.
How Mounjaro and Wegovy Work Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways in the body simultaneously. This combined action may help regulate appetite, reduce food cravings, and support feeling fuller after smaller meals.
Wegovy (semaglutide) is a GLP-1-only receptor agonist, activating a single hormone pathway. It works through similar appetite suppression and satiety mechanisms but without the additional GIP action.
In clinical trials, the SURMOUNT study (Mounjaro) showed average weight loss of 15–21% of body weight at maximum dose (15 mg), whilst the STEP trial (Wegovy) showed approximately 14.9% average weight loss at 2.4 mg. Both results were achieved alongside reduced-calorie diet and increased physical activity. Individual results vary significantly.
- Mounjaro: Once-weekly injection, doses 2.5 mg to 15 mg
- Wegovy: Once-weekly injection, doses 0.25 mg to 2.4 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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How to Buy: NHS vs Private Access in the UK
In the UK, both Mounjaro and Wegovy are prescription-only medicines requiring a clinical assessment before dispensing. NHS access is through tier 3 specialist weight management services following a GP referral, though availability and waiting times vary significantly by region. Private access is available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber — no NHS referral required.
Cost on the NHS is covered if prescribed through specialist services. Private costs vary by provider and dose but typically range from £129–£320 per month. Your prescriber will assess which medication suits your individual health profile, BMI, and any weight-related health conditions. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses, and our BMI calculator to check your starting point.
NHS eligibility includes adults with a BMI of 30 kg/m² or above, or BMI 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. South Asian, Chinese, Black African, and Black Caribbean adults may be eligible at lower BMI thresholds (from 27.5 kg/m²). Both medications are prescription-only and require an assessment to confirm suitability based on your individual medical history, other medications, and health profile.
- 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 main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP+GLP-1 agonist (two mechanisms), whilst Wegovy is a GLP-1-only agonist (one mechanism). Clinical trials show Mounjaro achieved slightly higher average weight loss (15–21%) than Wegovy (14.9%), though individual results vary. Both are once-weekly injections available as prescription-only medicines in the UK.
Can I buy Mounjaro or Wegovy without a prescription in the UK?
No. Both are prescription-only medicines in the UK. You must have a prescription from a UK-licensed prescriber following a clinical assessment. You can access this through NHS specialist weight management services (via GP referral) or privately through a registered online prescriber and GPhC pharmacy.
Which one is available on the NHS faster?
Both Mounjaro and Wegovy are available through NHS tier 3 specialist weight management services, but regional waiting times vary significantly. Some areas have waits of several months or longer. Private access through registered online prescribers is typically faster, though costs apply.
How do the doses compare between Mounjaro and Wegovy?
Mounjaro starts at 2.5 mg and goes up to 15 mg once weekly. Wegovy starts at 0.25 mg and goes up to 2.4 mg once weekly. Approximate equivalence suggests Mounjaro 5 mg ≈ Wegovy 0.5 mg, and Mounjaro 15 mg ≈ Wegovy 2.4 mg, though any switch must be managed by a prescriber.
Will my GP prescribe either of these directly?
Most GPs do not prescribe Mounjaro or Wegovy directly. NHS access is typically through referral to tier 3 specialist weight management services. Private access is through registered online prescribers (not your GP). Either way, a clinical assessment confirming eligibility and suitability is required before dispensing.
Ready to take control of your weight loss journey?
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