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 to Wegovy Conversion — Dose Equivalence Explained
If you're switching from Mounjaro (tirzepatide) to Wegovy (semaglutide), or comparing the two weight loss injections, understanding approximate dose equivalence is important. Both are prescription-only GLP-1 medications licensed in the UK for weight management, but they work slightly differently and have different dose ranges. This guide explains the approximate conversion, the key differences between them, and why any switch must be managed by your prescriber. Use our free GLP-1 weight loss calculator to estimate potential weight loss outcomes with either medication.
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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/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 and Wegovy Doses Compare
Mounjaro (tirzepatide) and Wegovy (semaglutide) are not directly equivalent — there is no official NHS or MHRA conversion chart. However, clinical practice and the SURMOUNT and STEP trial data provide approximate guidance:
- Mounjaro 5 mg ≈ Wegovy 0.5 mg — both early maintenance doses with similar early weight loss effects
- Mounjaro 10 mg ≈ Wegovy 1.7 mg — mid-range doses with more significant effects
- Mounjaro 15 mg ≈ Wegovy 2.4 mg — maximum doses showing comparable clinical outcomes
In clinical trials, Mounjaro at 15 mg produced average weight loss of approximately 20.9% body weight, while Wegovy at 2.4 mg produced approximately clinically studied weight loss. These are averages only — individual results vary considerably. Any switch between medications must be managed by your prescriber, who will assess your response and adjust accordingly. The KwikPen device used for Mounjaro differs from Wegovy's pen design, so injection technique remains consistent with whichever medication you are prescribed.
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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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Key Differences Between Mounjaro and Wegovy
The fundamental difference is mechanism of action. Mounjaro is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways simultaneously, which may explain its slightly higher average weight loss in clinical trials. Wegovy is a GLP-1 receptor agonist only — it activates one pathway. Both slow gastric emptying and reduce appetite, but the dual mechanism of Mounjaro may offer additional metabolic benefits for some patients. Side effects are similar (nausea, diarrhoea, constipation most common), though individual tolerance varies. Eligibility criteria are identical in the UK — BMI ≥30, or BMI 27–29.9 with weight-related health conditions. Your GP or prescriber will assess which is more suitable based on your individual health profile, previous medication responses, and medical history. Both require ongoing clinical review and a commitment to dietary changes and increased physical activity.
- 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 there an official Mounjaro to Wegovy conversion chart?
No. There is no official NHS or MHRA conversion chart. The approximate equivalences (5 mg ≈ 0.5 mg, 10 mg ≈ 1.7 mg, 15 mg ≈ 2.4 mg) are based on clinical trial data and prescriber experience. Any switch must be managed by your prescriber, who will consider your individual response and adjust doses appropriately.
Why does Mounjaro show more weight loss than Wegovy in trials?
Mounjaro's dual GIP and GLP-1 mechanism may provide additional metabolic effects compared to Wegovy's single GLP-1 pathway. However, individual results vary significantly. Trial averages do not predict personal outcomes — some people lose more on Wegovy, some on Mounjaro.
Can I switch from Mounjaro to Wegovy myself?
No. Any medication switch must be prescribed and managed by your GP or licensed prescriber. They will assess your response to Mounjaro, consider why a switch is being considered, and gradually transition you to the new medication with appropriate dose titration.
Which medication is better for weight loss — Mounjaro or Wegovy?
Neither is universally "better." Mounjaro showed slightly higher average weight loss in trials, but Wegovy is effective for many people. Suitability depends on your individual health, comorbidities, side effect tolerance, and prescriber assessment. Your prescriber will recommend the most appropriate option for you.
Are Mounjaro and Wegovy available on the NHS in the UK?
Yes, both are NHS-available through specialist tier 3 weight management services, subject to regional availability and NICE approval. Waiting lists vary by area. Both are also available privately through online prescription services following clinical assessment. ```
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