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 Injection For Diabetes — How It Compares To Wegovy
Mounjaro (tirzepatide) and Wegovy (semaglutide) are both prescription-only weekly weight loss injections available in the UK, but they work through different mechanisms. If you have diabetes or are overweight with diabetes-related health concerns, understanding how these medications differ can help you and your GP or prescriber make an informed choice. Both are licensed for weight management in UK adults, though access routes and eligibility vary. This guide compares the key differences in how they work, their clinical trial results, and what that means for you.
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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 is a dual GIP and GLP-1 receptor agonist, meaning it activates two separate hormone pathways in the body. GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) both help regulate appetite, reduce cravings, and slow how quickly food leaves your stomach. This dual action is what distinguishes Mounjaro from other weight loss injections available in the UK.
Wegovy is a GLP-1 receptor agonist only, activating just the single GLP-1 hormone pathway. While this is a well-established and effective mechanism, it does not target the GIP pathway that Mounjaro addresses.
- Mounjaro (tirzepatide): Dual mechanism, maximum dose 15 mg once weekly
- Wegovy (semaglutide): Single mechanism, maximum dose 2.4 mg once weekly
- Clinical trials: SURMOUNT (Mounjaro) vs STEP (Wegovy) — different study designs, different populations
Both are administered as a KwikPen auto-injection once per week. Neither is insulin, though both help improve blood sugar control as a secondary benefit when used for weight management.
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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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Clinical Trial Data And Weight Loss Results
In the SURMOUNT-1 trial, participants on Mounjaro 15 mg achieved an average weight loss of approximately 20.9% of body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity. The STEP-1 trial showed Wegovy 2.4 mg users achieved approximately clinically studied weight loss over 68 weeks under similar conditions.
Important context: These are clinical trial averages — individual results vary significantly. The difference in average weight loss between trials cannot be directly compared, as they used different populations, timescales, and study protocols. Your personal results depend on your starting weight, adherence, diet, exercise, genetics, and overall health. A prescriber will discuss expected outcomes during your clinical assessment and help you set realistic goals. Track your progress using our free weight loss calculator and progress tracker to monitor your actual results over time.
- 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 approved for diabetes in the UK?
Mounjaro is approved for weight management in UK adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions (including type 2 diabetes). It is not specifically a diabetes medication like Ozempic, but weight loss often improves blood sugar control. A prescriber will assess whether it is suitable for your individual situation.
Which injection is more effective for weight loss?
Clinical trials suggest Mounjaro (at maximum dose) achieved slightly higher average weight loss than Wegovy in their respective studies. However, individual responses vary considerably. Some people respond better to one than the other. Your prescriber will help determine which is more appropriate based on your medical history, current medications, and personal health goals.
Can I switch from Wegovy to Mounjaro if I'm already on Wegovy?
Yes, switching between GLP-1 medications is possible, but it must be managed by your prescriber. There is no official established conversion chart — approximate equivalences exist (e.g., Wegovy 2.4 mg roughly corresponds to Mounjaro 10–15 mg), but the switch requires individual medical assessment and titration.
How do I access Mounjaro or Wegovy on the NHS in the UK?
Both medications are available through NHS specialist tier 3 weight management services via GP referral. Availability and waiting times vary significantly by region. Private access is available through GPhC-registered online pharmacies following an online clinical assessment. Neither is available as a routine GP prescription outside specialist services.
What's the difference between Mounjaro and Ozempic?
Ozempic (semaglutide) is licensed for type 2 diabetes management in the UK. Mounjaro is licensed for weight management. Both contain different medications with different mechanisms. Ozempic is not licensed for weight loss in the UK — using it off-label for weight loss is not recommended. Wegovy is the licensed weight management version of semaglutide, available at the 2.4 mg dose.
Ready to take control of your weight loss journey?
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