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
Free tracker included with every download this week
What Is Mounjaro Medicine?
Mounjaro (tirzepatide) is a prescription-only medicine licensed in the UK for weight management in adults. It's a once-weekly injectable medication that works differently to other weight loss treatments because it activates two natural hormone pathways — GIP and GLP-1 — rather than just one. This dual action may help regulate appetite, reduce food cravings, and support feeling fuller after smaller meals. Like all prescription weight loss medications, Mounjaro is used alongside a reduced-calorie diet and increased physical activity, not instead of them. Understanding how this medicine works and whether it might be suitable for you is an important first step.
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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 Medicine Works
Mounjaro's dual mechanism sets it apart from other weight management medicines. It activates both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) — two natural hormones your body produces after eating.
- GLP-1 action: Signals to your brain that you're full, reducing appetite and food cravings
- GIP action: Supports energy regulation and fat utilisation
- Gastric effect: Slows how quickly food leaves your stomach, helping you feel satisfied longer
Unlike Wegovy (semaglutide), which activates GLP-1 only, Mounjaro's dual approach may help some people achieve greater weight loss in clinical trials. Individual results vary significantly, and this medicine is not insulin — it works on appetite and hormone regulation, not blood sugar control directly. Mounjaro is dispensed as a KwikPen — a pre-filled injection pen you use at home once weekly.
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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.
Mounjaro Eligibility, Doses & How to Access It
In the UK, you may be eligible for Mounjaro if you have a BMI of 30 or above, or a BMI of 27–29.9 with at least one weight-related health condition (type 2 diabetes, high blood pressure, sleep apnoea, or cardiovascular disease). Lower BMI thresholds apply for adults of South Asian, Chinese, Black African, or Black Caribbean heritage — often starting at BMI 27.5.
Mounjaro doses range from 2.5 mg to 15 mg, given once weekly by injection. Treatment starts at 2.5 mg and increases gradually over weeks. Access is through NHS specialist weight management services (typically with long waiting lists) or private online prescribing following a clinical assessment. A licensed prescriber will assess your individual health to determine suitability. Use our free BMI calculator above to check your current BMI, and our GLP-1 weight loss calculator to explore potential weight loss projections.
- 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 the same as Ozempic?
No. Both Mounjaro and Ozempic are different medications. Mounjaro (tirzepatide) is specifically licensed for weight management in the UK. Ozempic (also semaglutide) is approved for type 2 diabetes management at lower doses. They have different mechanisms, doses, and licensed uses — only Mounjaro is the approved weight management version.
What results can I expect from Mounjaro?
Clinical trials (SURMOUNT-1) showed average weight loss of 15–21% of body weight over 72 weeks, alongside diet and exercise. However, individual results vary significantly — some people lose more, some less. Weight loss is not assured. Results depend on adherence, lifestyle changes, and individual metabolism.
What are the main side effects of Mounjaro?
Very common side effects include nausea, diarrhoea, vomiting, and constipation — typically mild and temporary. Less common are headache, fatigue, and injection site reactions. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and allergic reactions. Always inform your prescriber of any concerning symptoms.
How do I get Mounjaro prescribed in the UK?
You can access Mounjaro through NHS specialist tier 3 weight management services (referral from your GP, but waiting lists vary by region) or through private online prescribing with a UK-licensed prescriber following a clinical assessment. Private access is typically faster but involves a cost.
Can I switch from Wegovy to Mounjaro?
Yes, switching between weight loss medications is possible and may be managed by a prescriber. Approximate dose equivalences exist, but any switch must be supervised by a healthcare professional. Discuss with your prescriber whether switching might be beneficial for you.
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.