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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Eli Lilly's Mounjaro in the UK โ What You Need to Know
Mounjaro (tirzepatide) is a prescription-only weight management injection manufactured by Eli Lilly and Company, approved for use in the UK. It works as a dual GIP and GLP-1 receptor agonist, which means it activates two natural hormone pathways to help regulate appetite and support feeling fuller after meals. This guide explains how Mounjaro works, who is eligible, how NHS and private access work, and what to expect from treatment. If you're considering weight loss options in the UK, understanding Mounjaro is an important starting point.
10,000+ calculations today ยท NHS-aligned thresholds ยท 100% free
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/mยฒ).
While BMI isn't a perfect measure โ it doesn't account for muscle mass, bone density, or fat distribution โ 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 โ 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 Doses Available
Mounjaro is unique because it's a dual-action medication, combining GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 receptor agonist effects. This dual mechanism may help regulate appetite, reduce food cravings, and slow gastric emptying. The medication comes as a pre-filled KwikPen device for once-weekly injections into the stomach, thigh, or upper arm.
Dose progression is gradual. You start with 2.5 mg weekly for 4 weeks, then escalate to 5 mg, 7.5 mg, 10 mg, 12.5 mg, and finally up to 15 mg (the maximum). Each dose is held for at least 4 weeks before increasing. In clinical trials (SURMOUNT-1), participants on Mounjaro lost an average of 15% body weight at 5 mg, 19.5% at 10 mg, and 20.9% at 15 mg โ though individual results vary significantly. Weight loss occurred alongside a reduced-calorie diet and increased physical activity.
You can track your weight loss progress and estimate potential outcomes using our free GLP-1 weight loss calculator, which helps visualise results at different doses.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care โ from a UK-regulated online pharmacy.
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 โ 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 โ completely free.
UK Eligibility, NHS Access, and Private Options
You may be eligible for Mounjaro if you have a BMI of 30 or above, or 27โ29.9 with a weight-related health condition such as type 2 diabetes, prediabetes, high blood pressure, sleep apnoea, or cardiovascular disease. For adults of South Asian, Chinese, Black African, or Black Caribbean backgrounds, lower BMI thresholds may apply (27.5 or above). You cannot take Mounjaro if you're under 18, pregnant, breastfeeding, or allergic to tirzepatide.
NHS access is through specialist tier 3 weight management services via GP referral โ NICE has approved tirzepatide for NHS use, but regional availability and waiting lists vary significantly. Private access is available through GPhC-registered online pharmacies following a clinical assessment by a UK-licensed prescriber. Check your BMI using our free BMI calculator to understand your starting point, and discuss options with your GP or a private prescriber.
- 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 โ 5mg โ 7.5mg โ 10mg โ 12.5mg โ 15mg
- GLP-1 receptor agonist
- Up to 15โ17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg โ 0.5mg โ 1mg โ 1.7mg โ 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 | 15โ22.5% | 12โ17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20โ32 weeks | 16โ20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | ยฃ150โยฃ250/month | ยฃ150โยฃ300/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 โ 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 semaglutide, but Ozempic is approved for type 2 diabetes (up to 2 mg). Mounjaro contains tirzepatide, a different medication. Mounjaro is a dual GIP and GLP-1 agonist, whereas Ozempic is GLP-1 only. Mounjaro is licensed specifically for weight management in the UK at higher doses (up to 15 mg).
How quickly will I lose weight on Mounjaro?
Weight loss varies between individuals, but typically begins within the first few weeks. In clinical trials, average weight loss was 15โ21% of body weight over 72 weeks, depending on dose. Results are best with a reduced-calorie diet and increased physical activity. Your GP can discuss realistic expectations for your situation.
What are the main side effects of Mounjaro?
Very common side effects include nausea, diarrhoea, vomiting, and constipation. These usually improve over time as your body adjusts. Less common side effects are fatigue, dizziness, and hair loss. Serious but rare complications include pancreatitis and gallbladder problems. Always report persistent or severe symptoms to your prescriber immediately.
Can I switch from Wegovy to Mounjaro?
Yes, switching is possible, but must be managed by your prescriber. Mounjaro (tirzepatide) and Wegovy (semaglutide) are different medications with different mechanisms. Approximate dose equivalences exist (e.g., 5 mg Mounjaro โ 0.5 mg Wegovy), but there's no official conversion chart. Your prescriber will guide any switch based on your individual response and tolerability.
Do I need to stay on Mounjaro forever?
No. Mounjaro is not a lifetime commitment. However, most people regain weight if they stop treatment without maintaining dietary and lifestyle changes. Your prescriber will help determine how long you should continue. The goal is to combine medication with sustainable habit changes so you can maintain weight loss long-term.
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.