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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Which Is Safer: Mounjaro Or Wegovy in the UK?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management medications approved by UK regulatory bodies and NICE for NHS use. Neither is definitively "safer" than the other — safety depends on individual health factors and how well you tolerate each medication. Both have been studied extensively in clinical trials and show similar safety profiles overall, though they work slightly differently. Your GP or prescriber will assess which is more suitable for you based on your medical history, current medications, and personal circumstances. Understanding how they compare helps you have an informed conversation with your healthcare team.
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Calculate Your BMI Instantly
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.
NHS Approval, MHRA Status, and Clinical Evidence
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist approved by NICE for weight management in UK adults. It carries additional MHRA monitoring (Black Triangle ▼ status) as it is a newer medication class. Mounjaro is available through NHS tier 3 specialist weight management services, though regional availability varies significantly.
Wegovy (semaglutide) is a GLP-1 receptor agonist that has been prescribed for longer and is also approved by NICE for weight management in the UK. Wegovy has an established safety record across the STEP clinical trials.
- Both medications have undergone rigorous safety monitoring through UK regulatory processes
- SURMOUNT trial data (Mounjaro) showed average weight loss of 15–21% body weight alongside reduced-calorie diet and exercise
- STEP trial data (Wegovy) showed average weight loss of approximately 15% body weight under similar conditions
- Both carry similar common side effects: nausea, diarrhoea, vomiting, constipation, and stomach pain
- Individual tolerance varies — some people tolerate one medication better than the other
Neither has been proven superior in terms of safety; prescriber choice often depends on individual suitability and availability.
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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.
NHS Access, Eligibility, and Private Routes in the UK
In the UK, both medications are available through NHS specialist tier 3 weight management services and through private online prescribing from GPhC-registered pharmacies. NHS access involves referral from your GP and clinical assessment by a specialist, though waiting lists can be long in many regions. Private prescribing is faster but requires payment.
Eligibility for both Mounjaro and Wegovy is the same: BMI ≥30, or BMI 27–29.9 with weight-related health conditions such as type 2 diabetes, prediabetes, high blood pressure, or cardiovascular disease. Lower thresholds apply for South Asian, Chinese, Black African, or Black Caribbean adults (BMI ≥27.5). Use our free BMI calculator to check your personal BMI, then discuss options with your GP. Both medications are prescription-only and require ongoing clinical assessment; they are not suitable during pregnancy or breastfeeding.
- 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 or Wegovy safer to use long-term?
Both are designed for long-term use and have safety data supporting this in clinical trials. Mounjaro has additional MHRA monitoring due to being newer. Long-term safety depends on individual tolerance, adherence to reduced-calorie diet and exercise, and regular monitoring by your prescriber. Neither is universally "safer" — individual response varies significantly.
Which has fewer side effects, Mounjaro or Wegovy?
Both medications share very common side effects (nausea, diarrhoea, constipation, stomach pain). Some people tolerate one better than the other, but clinical trials show similar overall side effect profiles. Side effects typically improve over time as your body adjusts. Your prescriber can help manage these through dose adjustment if needed.
Can I switch from Mounjaro to Wegovy on the NHS?
Switching between medications is possible but requires prescriber approval and clinical reassessment. There is no official NHS conversion chart between Mounjaro and Wegovy — any switch must be managed individually by your specialist tier 3 weight management service. Discuss options with your prescriber if one medication is not working well for you.
What does MHRA Black Triangle status mean for Mounjaro?
Black Triangle (▼) status means the MHRA is monitoring Mounjaro more closely as a newer medication. This does not mean it is unsafe — it means post-approval safety data is still being collected. It reflects standard practice for new medication classes in the UK and allows for rapid identification of any emerging safety concerns.
Which medication does the NHS recommend more — Mounjaro or Wegovy?
NICE has approved both Mounjaro and Wegovy for NHS use under the same eligibility criteria. NICE has not recommended one over the other — both are equally approved options. Your NHS prescriber will choose based on your individual health profile, any contraindications, and local service protocols. Private prescribers also offer both options.
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.