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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Pros and Cons of Mounjaro in the UK
Mounjaro (tirzepatide) is a prescription weight loss injection available in the UK that works differently from other GLP-1 medications. Understanding its advantages and disadvantages can help you make an informed decision about whether it might be suitable for you. This guide compares Mounjaro's benefits and drawbacks, including how it stacks up against alternatives like Wegovy. Always consult your GP or a licensed prescriber before deciding on any weight management treatment.
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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 — Advantages and Disadvantages
Key advantages of Mounjaro:
- Dual mechanism — activates both GIP and GLP-1 receptors (unlike Wegovy which targets GLP-1 only), potentially offering stronger appetite suppression
- Once-weekly KwikPen injection — convenient and easy to use at home
- Clinical trial data showed average weight loss of 15–21% of body weight over 72 weeks when combined with diet and exercise
- Available through NHS specialist weight management services and private prescription routes
- Dose titration flexibility — five dose levels (2.5 mg to 15 mg) allow personalised adjustment
Key disadvantages:
- Common side effects including nausea, diarrhoea, vomiting, and constipation — especially during dose escalation
- Requires minimum 4 weeks at each dose before increasing, making the titration schedule longer than some alternatives
- Cost — private prescriptions typically range from £200–£300 per month depending on dose
- Individual results vary significantly — not everyone achieves the average weight loss shown in clinical trials
- Requires ongoing prescription and clinical monitoring from a licensed prescriber
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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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Mounjaro vs Wegovy — Which Might Suit You Better?
Both Mounjaro and Wegovy are prescription weight loss injections licensed in the UK, but they differ in mechanism and dosing. Mounjaro uses a dual GIP and GLP-1 approach which may provide stronger appetite control, whilst Wegovy uses GLP-1 only. Clinical trial data shows Mounjaro achieved slightly higher average weight loss (20.9% at maximum dose) compared to Wegovy (14.9%), though individual outcomes vary. Both require a clinical assessment to determine suitability based on your BMI, health conditions, and medical history. Your prescriber will discuss which option — if either — is appropriate for you. Use our free GLP-1 weight loss calculator to explore projected results at different dose levels, and our BMI calculator to understand your starting point.
- 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 available on the NHS in the UK?
Mounjaro (tirzepatide) is approved by NICE for use within NHS specialist weight management services. However, NHS availability varies significantly by region and waiting lists can be substantial. Access is typically through tier 3 specialist services rather than standard GP prescription. Private prescription through a licensed prescriber is an alternative route if NHS access is limited in your area.
What are the most common side effects of Mounjaro?
Very common side effects include nausea, diarrhoea, vomiting, and constipation — particularly during the first few weeks and when increasing doses. Most side effects are mild to moderate and tend to improve over time. Serious side effects are rare but can include severe stomach pain (possible pancreatitis) or severe allergic reactions. Always report persistent or concerning symptoms to your prescriber.
How much weight can you lose on Mounjaro UK?
Clinical trials (SURMOUNT-1) showed average weight loss of approximately 15% at 5 mg, 19.5% at 10 mg, and 20.9% at 15 mg over 72 weeks, alongside a reduced-calorie diet and increased physical activity. However, individual results vary considerably — some people lose more, others less. Your prescriber can discuss realistic expectations based on your personal circumstances.
How does Mounjaro dose titration work in the UK?
Mounjaro uses a gradual dose escalation schedule: you start at 2.5 mg weekly for 4 weeks, then increase to 5 mg, then 7.5 mg, 10 mg, 12.5 mg, and finally 15 mg (the maximum). Each dose level is maintained for a minimum of 4 weeks. This slower titration allows your body to adjust and helps manage side effects, though it means reaching the maximum dose takes about 20 weeks.
Can I switch from Mounjaro to Wegovy or vice versa?
Switching between weight loss injections is possible but must be managed by your prescriber. There is no official established conversion formula — approximate equivalences exist based on clinical practice (e.g., Mounjaro 15 mg is roughly equivalent to Wegovy 2.4 mg), but your prescriber will assess your individual situation before switching. Never stop one medication and start another without medical guidance.
Ready to take control of your weight loss journey?
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