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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Should I Switch From Mounjaro To Wegovy?
Whether switching from Mounjaro to Wegovy is right for you depends on how well you're responding to your current treatment, any side effects you're experiencing, and your individual health goals. Both are prescription-only GLP-1 medications licensed in the UK for weight management, but they work slightly differently. Your GP or prescriber should guide any decision to switch between them, as this requires a clinical reassessment rather than a simple change. This guide explains the key differences to help you have an informed conversation with your healthcare team.
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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.
Key Differences Between Mounjaro and Wegovy
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two separate hormone pathways in the body. This dual mechanism may explain why clinical trials showed an average weight loss of around 15–21% of body weight at the highest dose.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single hormone pathway. STEP trial data showed an average weight loss of approximately 14.9% of body weight at the highest maintenance dose (2.4 mg).
- Starting dose: Mounjaro 2.5 mg vs Wegovy 0.25 mg
- Maximum dose: Mounjaro 15 mg vs Wegovy 2.4 mg
- Injection frequency: Both once weekly
- Approximate equivalent doses: Mounjaro 10 mg ≈ Wegovy 2.4 mg (though no official conversion exists)
Individual results vary significantly — the clinical trial averages don't predict your personal outcome. Your weight loss depends on genetics, lifestyle changes, adherence, and how your body responds to the medication.
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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.
When Switching Might Be Considered
You might discuss switching with your GP or prescriber if you're not seeing expected weight loss results after several months at your current dose, experiencing unmanageable side effects, or if your health circumstances change. Some people find they tolerate one medication better than another.
However, switching is not a simple swap — it requires a new clinical assessment because the medications have different dosing schedules, side effect profiles, and mechanisms. Your prescriber will need to reassess your eligibility, manage any overlap in dosing, and monitor you closely during a transition period. Never switch between medications without medical guidance, even if you have spare pens or doses remaining.
Using our GLP-1 weight loss calculator can help you understand potential weight loss projections with either medication, though these are estimates based on trial averages and your actual results may differ.
- 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 I just switch from Mounjaro to Wegovy myself?
No — both are prescription-only medications. Switching requires a new prescription and clinical assessment from your GP or licensed prescriber. They need to check your current health status, how you've responded to Mounjaro, and whether Wegovy is appropriate for you. Never change medications without medical guidance.
If Mounjaro is dual-action, is it automatically better than Wegovy?
Not necessarily. While Mounjaro's dual GIP and GLP-1 mechanism showed slightly higher average weight loss in trials (15–21% vs 14.9%), individual results vary significantly. Some people lose more on Wegovy, and tolerability matters — the medication you tolerate best and stick with long-term may be the more effective choice for you personally.
What's the approximate equivalent dose if I switch from Mounjaro to Wegovy?
Mounjaro 10 mg is roughly equivalent to Wegovy 2.4 mg (maximum dose), and Mounjaro 5 mg is approximately equivalent to Wegovy 0.5–1 mg. However, there is no official conversion chart. Your prescriber will not simply convert your dose — they'll restart Wegovy at the lowest dose and titrate upwards over several weeks, monitoring your response.
Will I lose more weight if I switch to Wegovy from Mounjaro?
Clinical trial data suggests Mounjaro may produce slightly higher average weight loss, but individual results vary substantially. Some people achieve better results and tolerability on Wegovy. Weight loss depends more on your personal response, lifestyle adherence, and how long you've been on your current dose than on switching medications.
How long does it take to see results after switching from Mounjaro to Wegovy?
If you switch, you'll restart at Wegovy's lowest dose (0.25 mg) and titrate upwards over 16+ weeks to reach the maintenance dose of 2.4 mg. This means it typically takes 4–5 months to reach full dosing. Weight loss may take several weeks to become noticeable, so patience is important during a medication transition.
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.