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 for Diabetes Dose vs Wegovy — UK Guide
Mounjaro (tirzepatide) and Wegovy (semaglutide) are both GLP-1 based prescription injections used for weight management in the UK, and both may be used in adults with type 2 diabetes. However, they work differently and have different dosing schedules. Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy is a GLP-1 only receptor agonist. Understanding the dosing differences and clinical trial data can help you and your GP decide which prescription medication might be suitable for your individual health needs. This guide compares both medicines factually, focusing on UK eligibility and dosing context.
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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.
Dosing Schedules and Clinical Trial Data
Mounjaro (tirzepatide) starts at 2.5 mg once weekly and escalates in 4-week intervals: 5 mg, 7.5 mg, 10 mg, 12.5 mg, and finally 15 mg. In the SURMOUNT-1 clinical trial, participants on Mounjaro 15 mg achieved average weight loss of approximately 20.9% of body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity. Mounjaro works by activating both GIP and GLP-1 pathways, which may provide dual appetite and metabolic regulation.
Wegovy (semaglutide) starts at 0.25 mg once weekly and escalates more gradually: 0.5 mg, 1 mg, 1.7 mg, and maximum 2.4 mg. In the STEP-1 clinical trial, Wegovy 2.4 mg achieved average weight loss of approximately 14.9% of body weight over 68 weeks, also alongside lifestyle changes. Wegovy activates the GLP-1 pathway only.
Individual results vary significantly. Both medications require a clinical assessment before prescription and must be used with dietary and lifestyle changes, not as standalone treatments.
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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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Eligibility, Suitability, and Prescriber Assessment
Both Mounjaro and Wegovy are prescription-only in the UK and require a clinical assessment to determine suitability. Eligibility typically includes: BMI of 30 kg/m² or above, or BMI of 27–29.9 kg/m² with weight-related health conditions such as type 2 diabetes, prediabetes, high blood pressure, or cardiovascular disease. Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may be eligible at lower BMI thresholds (from 27.5 kg/m²).
Your prescriber will assess which medicine is appropriate for you based on your individual health history, current medications, and how your body may respond. There is no established official conversion between Mounjaro and Wegovy doses — any switch between medications must be managed by your prescriber. Use our free GLP-1 weight loss calculator to estimate potential weight loss at different doses, and our BMI calculator to check your current BMI and eligibility range.
- 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 better than Wegovy for diabetes?
Clinical trial data suggests Mounjaro may produce slightly higher average weight loss (approximately 20.9% vs 14.9%), but individual results vary significantly. Both medications work and both are suitable for adults with type 2 diabetes. Your prescriber will assess which is more appropriate for you based on your health profile, other medications, and individual factors. Neither is universally "better" — suitability depends on your specific situation.
What is the starting dose of Mounjaro for diabetes?
Mounjaro starts at 2.5 mg once weekly, regardless of whether it's being used for weight management or diabetes-related weight loss. The dose is increased by 2.5 mg every 4 weeks until reaching an effective dose, up to a maximum of 15 mg weekly. Your prescriber will determine the right dose escalation schedule for you based on how you respond and tolerate the medication.
Can I switch from Wegovy to Mounjaro?
Yes, you can switch between medications under prescriber guidance, but there is no official established dose conversion chart. Approximate equivalence is often used in clinical practice (for example, Wegovy 2.4 mg is sometimes considered roughly equivalent to Mounjaro 10–15 mg), but this is not absolute. Any switch must be managed by your prescriber, who will advise on timing and dosing.
How long does it take to see results with Mounjaro?
Weight loss typically begins within the first 4–8 weeks of starting Mounjaro, though this varies between individuals. Most significant weight loss occurs between weeks 8 and 20. Results depend on adherence to reduced-calorie diet and physical activity alongside the medication. Some people see results faster than others — your prescriber can discuss realistic timelines for you.
Is Mounjaro available on the NHS for type 2 diabetes?
Mounjaro is NICE-approved and available through NHS specialist weight management services (tier 3/4), but availability and wait times vary significantly by region. Your GP can refer you to your local specialist weight management service if you're eligible. Private prescription is also available through online clinical assessment if NHS access is limited in your area.
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