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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Switching From Wegovy To Mounjaro — What You Need To Know
If you're currently taking Wegovy (semaglutide) and considering switching to Mounjaro (tirzepatide), you're not alone — many people explore alternatives to find what works best for their weight management. Both are prescription-only GLP-1 and GIP/GLP-1 receptor agonist medications licensed for weight management in the UK, but they work slightly differently and have different dosing schedules. This guide explains the key differences, approximate dose equivalence, what to expect during a switch, and how to discuss this with your prescriber. Always consult your GP or weight management specialist before making any changes to your medication.
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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 Wegovy And Mounjaro
Wegovy (semaglutide) is a GLP-1 receptor agonist — it activates a single hormone pathway that reduces appetite and helps you feel fuller after smaller meals. Maximum dose is 2.4 mg once weekly. In the STEP clinical trials, people taking Wegovy lost an average of around 15% of their body weight over 68 weeks, alongside diet and exercise changes.
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways, which may offer a different mechanism of action. Maximum dose is 15 mg once weekly. In SURMOUNT clinical trials, people taking Mounjaro lost an average of 15–21% of their body weight at different doses, though individual results vary significantly.
Both are prescription-only and require an initial clinical assessment. The choice between them depends on individual response, tolerability, and prescriber assessment. If Wegovy hasn't delivered the results you hoped for, or if you're experiencing troublesome side effects, switching may be worth discussing with your prescriber.
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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.
Approximate Dose Equivalence And Transition
While there is no official conversion chart between Wegovy and Mounjaro, clinical practice suggests approximate equivalences based on clinical trial efficacy data:
- Wegovy 0.5 mg ≈ approximately Mounjaro 5 mg
- Wegovy 1.7 mg ≈ approximately Mounjaro 10 mg
- Wegovy 2.4 mg ≈ approximately Mounjaro 15 mg
These are approximate only — your prescriber may start you on a lower Mounjaro dose (2.5 mg) to assess tolerability, even if you were on a higher Wegovy dose. The transition typically involves stopping your current Wegovy dose and beginning Mounjaro at a starting dose, then titrating up weekly as directed. Your prescriber will monitor your response and side effects closely during the switch. Never attempt to self-adjust doses or skip doses during a medication change.
During the transition, you may experience a period where you're not on either medication (typically no more than a week between your last Wegovy dose and your first Mounjaro dose). Some people notice appetite returning during this gap — this is normal. Use our free GLP-1 weight loss calculator to see projected weight loss at different Mounjaro doses once you and your prescriber agree on your new regimen. Keep a record of how you feel on each dose to help your prescriber find the right balance between efficacy and tolerability.
- 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.
Why would someone switch from Wegovy to Mounjaro?
People switch for several reasons: Wegovy may not have delivered the expected weight loss, side effects may be problematic, or they want to try the dual mechanism of Mounjaro. Some find Mounjaro's once-weekly dosing schedule more convenient if they're used to infrequent injections. Individual responses to medications vary — what works for one person may not work as well for another. Your prescriber will assess whether a switch is appropriate.
What's the difference between Mounjaro and semaglutide in Wegovy?
Wegovy contains semaglutide, a GLP-1 receptor agonist (single mechanism). Mounjaro contains tirzepatide, a dual GIP and GLP-1 receptor agonist (two mechanisms). The dual mechanism of Mounjaro may provide different appetite suppression and metabolic effects. Both are prescription-only and licensed for weight management in the UK — semaglutide at 2.4 mg (Wegovy) is the licensed weight management dose, distinct from Ozempic which is approved for diabetes.
Will I start Mounjaro at the same dose I was taking Wegovy?
Unlikely. Your prescriber will almost certainly start you on Mounjaro's lowest dose (2.5 mg) regardless of your Wegovy dose, to assess tolerability. This is because tirzepatide is a different medication with a different mechanism. You'll then titrate up weekly as directed. This cautious approach minimises the risk of severe nausea or other side effects during transition.
How long does it take to switch medications safely?
The actual switch typically takes 1–2 weeks: you'll stop Wegovy, wait until your next scheduled injection date (usually 7 days), then start Mounjaro. After that, you enter a 16–20 week dose titration phase as your prescriber gradually increases your Mounjaro dose. Never abruptly stop either medication without guidance — always follow your prescriber's specific transition plan.
Can I use my GLP-1 calculator to compare Wegovy and Mounjaro weight loss?
Yes — our free GLP-1 weight loss calculator on this page can help you project potential weight loss at different Mounjaro doses based on clinical trial data. Bear in mind that individual results vary significantly. Use the calculator alongside your prescriber's guidance to visualise what different doses might achieve, but remember that weight loss depends on many factors including adherence, diet, and exercise.
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.