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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Mounjaro vs Wegovy: Weight Loss Jab Comparison
Both Mounjaro and Wegovy are prescription-only weekly weight loss injections licensed in the UK, but they work in different ways and deliver different results. This guide compares the two medications side by side — including trial data, mechanisms, doses, and how to know which might be suitable for you. Individual suitability is assessed by your GP or a licensed prescriber following a clinical assessment. Try our free GLP-1 weight loss calculator above to see how these medications might fit into a weight loss plan.
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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. This dual mechanism may support stronger appetite reduction and help regulate how your body processes fat. Wegovy (semaglutide) is a GLP-1 receptor agonist only — it activates a single hormone pathway but is still highly effective for weight management.
In clinical trials, this mechanism difference showed measurable outcomes. The SURMOUNT trial for Mounjaro showed average weight loss of approximately 15–21% of body weight over 72 weeks at the highest dose (15mg). The STEP trial for Wegovy showed average weight loss of approximately 14.9% of body weight over 68 weeks at the maximum dose (2.4mg). Both are effective; individual results vary significantly based on lifestyle, adherence, and personal response.
- Mounjaro: Dual GIP + GLP-1 mechanism
- Wegovy: GLP-1 mechanism only
- Both are once-weekly injections
- Both require reduced-calorie diet and physical activity to maximise results
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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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Doses, Side Effects, and NHS Access
Mounjaro doses range from 2.5mg to 15mg weekly, with escalation every 4 weeks. Wegovy doses range from 0.25mg to 2.4mg weekly, with a longer escalation schedule. Both have similar common side effects — nausea, diarrhoea, constipation, and stomach pain are most frequent, typically mild, and often settle over time.
In the UK, both medications are available through NHS specialist weight management services (tier 3) and private online prescribing. NHS access requires referral from your GP and assessment by a specialist team — waiting times vary by region. Privately, both require an online clinical assessment with a UK-licensed prescriber. Your GP or prescriber will determine which medication is suitable based on your BMI, weight-related health conditions, and medical history. Use our free BMI calculator to check your starting point, and discuss with your healthcare provider which option may be appropriate for you.
- 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 is the main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 agonist (two hormone pathways), while Wegovy is a GLP-1 agonist only (single pathway). Both are weekly injections, but the dual mechanism in Mounjaro may produce slightly stronger appetite suppression. Individual response varies — one may suit you better than the other.
Which weight loss jab is more effective, Mounjaro or Wegovy?
In clinical trials, Mounjaro showed slightly higher average weight loss (15–21%) compared to Wegovy (14.9%), but differences are modest and individual results vary widely. Effectiveness depends on adherence, diet, exercise, and personal response. Your prescriber will assess which is most suitable for your situation.
Are the side effects different between these injections?
Side effects are very similar — both commonly cause nausea, diarrhoea, constipation, and stomach pain. These typically occur early and often improve with time. Serious side effects are rare. Always report unexpected symptoms to your prescriber immediately.
Can I get Mounjaro or Wegovy on the NHS in the UK?
Yes, both are available through NHS specialist weight management services, but access requires GP referral and assessment by a tier 3 service. Waiting lists vary by region. Both are also available privately through online clinical assessment with a UK-licensed prescriber.
How do I know which weight loss jab is right for me?
Your GP or licensed prescriber will assess your BMI, weight-related health conditions, medical history, and current medications. They will recommend which medication is most suitable. Use our free BMI calculator to check your starting point before your consultation.
Ready to take control of your weight loss journey?
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