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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Can Your GP Prescribe Mounjaro vs Wegovy?
If you're considering weight loss medication in the UK, your GP may recommend either Mounjaro (tirzepatide) or Wegovy (semaglutide) depending on your individual circumstances. Both are prescription-only GLP-1 medications, but they work differently and have different trial results. Understanding the key differences — including mechanism, dose range, and clinical evidence — can help you have an informed conversation with your prescriber about which might suit you best. This guide compares both medications factually to help you understand what your GP might consider.
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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.
Clinical Trial Data and How They Work Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways rather than one. The SURMOUNT-1 clinical trial showed that at the maximum 15 mg dose, participants lost an average of 20.9% of their body weight over 72 weeks, alongside diet and activity changes. At lower maintenance doses (5 mg and 10 mg), average losses were 15% and 19.5% respectively.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single hormone pathway. The STEP-1 trial showed an average weight loss of approximately 14.9% body weight at the maximum 2.4 mg dose over 68 weeks, also with diet and lifestyle changes.
- Mounjaro: dual mechanism, possibly stronger average results in trials
- Wegovy: single mechanism, well-established safety profile
- Both require clinical assessment — results vary significantly between individuals
Neither medication assures specific weight loss outcomes. Your GP will consider trial data alongside your personal health profile when recommending one over the other.
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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.
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Doses, Side Effects, and How Your GP Decides
Dose ranges: Mounjaro starts at 2.5 mg and titrates up to a maximum of 15 mg weekly. Wegovy starts at 0.25 mg and titrates to a maximum of 2.4 mg weekly. The Mounjaro kwikpen delivers higher maximum doses, which may be one factor your GP considers if you're responding slowly to lower doses.
Side effects are similar for both (nausea, diarrhoea, constipation), though individual tolerance varies. Your GP will assess your medical history, current medications, BMI, and any weight-related health conditions (like type 2 diabetes or hypertension) to decide which is more suitable. They'll also consider your preference, previous medication responses, and whether you're eligible for NHS or private prescription routes.
- 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.
Can my GP prescribe either medication, or does it matter which one?
Your GP can prescribe either Mounjaro or Wegovy if you're eligible (BMI 30+ or 27+ with weight-related health conditions). However, in many areas, GPs refer patients to specialist tier 3 weight management services, which then decide. Eligibility and availability vary significantly by region (ICB). Your GP will discuss which is more appropriate based on your health profile.
What's the main difference between Mounjaro and Wegovy mechanisms?
Mounjaro (tirzepatide) activates two hormone pathways — GIP and GLP-1 (dual agonist). Wegovy (semaglutide) activates GLP-1 only. The dual mechanism may explain why Mounjaro showed slightly higher average weight loss in trials, though both are effective and individual results vary considerably.
Which showed better weight loss results in clinical trials?
In clinical trials, Mounjaro at 15 mg averaged clinically studied weight loss; Wegovy at 2.4 mg averaged 14.9%. These are averages — individual outcomes vary significantly. Trial results don't predict your personal outcome. Use our free GLP-1 weight loss calculator to explore potential projected results at different doses.
How long does the GP prescription process take?
If referred to NHS specialist services, waiting times range from weeks to many months depending on your region. Private prescription (via online assessment with a UK-licensed prescriber) is typically faster — often within days. Both routes require a clinical assessment before prescription. Availability and timescales vary by area.
Will my GP choose based on NHS approval or cost?
NICE has approved both Mounjaro and Wegovy for NHS use within specialist weight management services, though regional availability varies. On the NHS, cost doesn't determine choice — your prescriber selects based on clinical suitability. Privately, both are available, with costs varying by dose and provider. Your GP will prioritise clinical fit over cost.
Ready to take control of your weight loss journey?
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