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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What Is Mounjaro Medication in the UK?
Mounjaro is a prescription-only weight management injection licensed in the UK that contains the active ingredient tirzepatide. It works differently from other weight loss medications because it's a dual GIP and GLP-1 receptor agonist—meaning it activates two natural hormone pathways to help regulate appetite and support weight loss alongside a reduced-calorie diet and increased physical activity. Understanding how this medication works, who's eligible, and what to expect can help you make informed decisions about your weight management options with your GP or healthcare professional.
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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 Works and UK Eligibility
Mounjaro (tirzepatide) activates two hormone receptors in your body: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual mechanism may help reduce appetite, decrease food cravings, and support feeling fuller after smaller meals. It also slows gastric emptying—how quickly food leaves your stomach—though this effect typically reduces over time.
In the UK, you may be eligible for Mounjaro if you have:
- A BMI of 30 kg/m² or above, or
- A BMI of 27–29.9 kg/m² with at least one weight-related health condition (type 2 diabetes, high blood pressure, high cholesterol, sleep apnoea, or cardiovascular disease)
If you're of South Asian, Chinese, Black African, or Black Caribbean descent, lower BMI thresholds may apply due to higher health risks at lower weights. A prescriber will assess your individual circumstances following a clinical consultation.
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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 Doses, Side Effects, and NHS Access
Mounjaro is given as a once-weekly injection using a pre-filled KwikPen. Treatment typically starts at 2.5 mg, increasing every 4 weeks to a maximum of 15 mg. In clinical trials, Mounjaro helped participants lose an average of 15–21% of their body weight over 72 weeks—though individual results vary significantly and weight loss occurs alongside lifestyle changes.
Common side effects include nausea, diarrhoea, vomiting, and constipation, which often improve over time. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and allergic reactions—seek immediate medical attention if these occur. Access to Mounjaro in the UK is through NHS specialist weight management services (with potential waiting lists) or private prescribing following an online 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 the same as Ozempic?
No. Both contain different active ingredients and are made by different manufacturers. Mounjaro (tirzepatide) is licensed for weight management, while Ozempic (insulin glargine) is licensed for type 2 diabetes. Mounjaro is a dual GIP/GLP-1 agonist, making it mechanically different from other weight loss medications.
How much weight can I expect to lose on Mounjaro?
Clinical trials showed an average weight loss of 15–21% of body weight over 72 weeks, but individual results vary significantly. Weight loss depends on your starting weight, dose, adherence to the medication, and lifestyle changes. Your GP can discuss realistic expectations for your circumstances.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro is approved by NICE for use within NHS specialist weight management services. Access requires referral from your GP to a tier 3 or tier 4 service, and availability varies significantly by region. Private prescribing is also available through registered online services.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1-only agonist. Mounjaro typically shows slightly higher average weight loss in trials, but both are effective. The choice depends on individual factors assessed by your prescriber. Use our GLP-1 weight loss calculator to explore potential outcomes at different doses.
Is Mounjaro safe for long-term use?
Clinical trials and ongoing monitoring data support Mounjaro as safe for long-term weight management when prescribed appropriately. However, it's not suitable during pregnancy, and certain medical conditions may restrict use. Your healthcare professional will assess whether it's safe and appropriate for you specifically.
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.