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 — Which Is Better?
There's no single "better" option between Mounjaro and Wegovy — both are prescription-only weight loss injections licensed in the UK, but they work differently and suit different people. Mounjaro (tirzepatide) uses a dual GIP and GLP-1 mechanism, while Wegovy (semaglutide) is a GLP-1-only medication. Both have shown clinically significant weight loss results, but individual response varies considerably. Your GP or prescriber will assess which is more appropriate based on your health, medical history, and personal circumstances. This guide compares both medications to help you understand the key differences.
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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 — The Key Difference
The fundamental difference between Mounjaro and Wegovy lies in their mechanism of action:
- Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist. It activates two natural hormone pathways simultaneously — GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual action may help regulate appetite more powerfully by working on two separate signalling systems in the brain.
- Wegovy (semaglutide) is a GLP-1-only receptor agonist. It activates the GLP-1 pathway alone, which still reduces appetite and supports feeling fuller after smaller meals, but through a single mechanism.
In clinical trials, Mounjaro demonstrated slightly higher average weight loss (approximately 15–21% of body weight) compared to Wegovy (approximately 15% on average) at maximum doses, though both were conducted alongside reduced-calorie diet and increased physical activity. However, individual results vary significantly — some people respond better to one medication than the other. Your prescriber can discuss which approach may be more suitable for you.
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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 Practical Differences
Dosing: Mounjaro starts at 2.5 mg and escalates to a maximum of 15 mg once weekly. Wegovy starts at 0.25 mg and reaches a maximum of 2.4 mg once weekly. Both use a KwikPen delivery device and are given once weekly, making them equally convenient.
Side effects: Both medications share common side effects — nausea, diarrhoea, constipation, and stomach pain are most frequent, particularly during dose escalation. Side effect profiles are comparable, though individual tolerance varies. Use our GLP-1 weight loss calculator to explore potential outcomes at different doses, and try the weight converter and BMI calculator to track where you currently sit on health guidelines.
Eligibility: Both are prescribed to adults with a BMI of 30 or above, or 27–29 with weight-related health conditions. Access in the UK is through NHS specialist services or private prescribing following 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 stronger than Wegovy?
Mounjaro showed slightly higher average weight loss in trials (up to 21% vs 15% for Wegovy), but both work through different mechanisms. "Stronger" isn't the right term — they're different. Some people respond better to the dual GIP/GLP-1 approach of Mounjaro, others do equally well on Wegovy's GLP-1-only mechanism. Your individual response is unpredictable and depends on your metabolism, not the medication alone.
Which has fewer side effects — Mounjaro or Wegovy?
Side effect profiles are very similar — both cause nausea, diarrhoea, and stomach discomfort most commonly, especially early on. Individual tolerance varies significantly. Neither is clearly "better" in terms of side effects. Your GP can discuss your tolerance history to help predict which you might manage better, but this is individual, not medication-specific.
Can I switch from Wegovy to Mounjaro if Wegovy isn't working?
Yes, switching between GLP-1 medications is possible and sometimes done in practice, though there's no official NHS conversion chart. Any switch must be managed by your prescriber — you shouldn't stop one and start another independently. Your prescriber can guide a safe transition if needed.
Is Mounjaro available on the NHS in the UK?
Mounjaro has been approved by NICE for weight management and is available through NHS specialist tier 3 weight management services, though availability and waiting times vary significantly by region. Private access is available through online prescribing. Wegovy is similarly available through both NHS specialist services and private channels.
What's the difference between Wegovy and Ozempic?
Both contain semaglutide, but Ozempic is licensed 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). Never use Ozempic for weight loss — only use Wegovy, which is prescribed specifically for this purpose.
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