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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Going From Mounjaro To Wegovy
Switching from Mounjaro (tirzepatide) to Wegovy (semaglutide) is a change between two different GLP-1 weight management medications that may be discussed with your GP or prescriber. Both are prescription-only injectables licensed in the UK, but they work differently and have different dosing schedules. Understanding why someone might switch, how doses compare, and what the transition involves can help you have an informed conversation with your healthcare provider about what's right for your individual situation.
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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.
How Mounjaro and Wegovy Differ
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist—meaning it activates two hormone pathways in the body. This dual mechanism may explain why clinical trials showed an average weight loss of around 15–21% body weight over 72 weeks at the maximum 15 mg dose.
Wegovy (semaglutide) is a single GLP-1 receptor agonist, activating only the GLP-1 pathway. The STEP-1 clinical trial showed an average weight loss of approximately 14.9% body weight at 68 weeks on the maximum 2.4 mg dose. Individual results vary significantly.
- Injection frequency: Both are once weekly
- Dose range: Mounjaro 2.5–15 mg; Wegovy 0.25–2.4 mg
- Side effect profile: Both commonly cause nausea, diarrhoea, and appetite changes—though tolerability varies between individuals
Some people switch medications if they experience intolerable side effects on one, or if their prescriber believes a different mechanism may be more effective for their individual response.
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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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Approximate Dose Equivalence and Transition
While there is no officially established conversion between Mounjaro and Wegovy doses, clinical practice suggests approximate equivalences:
- Mounjaro 5 mg ≈ Wegovy 0.5 mg
- Mounjaro 10 mg ≈ Wegovy 1.7 mg
- Mounjaro 15 mg ≈ Wegovy 2.4 mg
Important: These are approximations only—individual response varies. Any switch between medications must be managed by your prescriber, who will assess your current dose, response, and tolerance. You will not simply switch directly; your GP or specialist will likely restart you at a lower Wegovy dose and titrate up gradually, just as you would with a new medication. Allow time for your body to adjust to the new injection.
- 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 switch from Mounjaro to Wegovy without stopping first?
Your prescriber will advise on the transition timeline. You should not stop one and immediately start the other without clinical guidance. Some clinicians may overlap doses briefly; others may recommend a short break. This depends on your current dose, how you tolerate it, and the reason for switching. Always follow your prescriber's specific instructions.
Will I lose more weight on Wegovy than Mounjaro?
Clinical trial data shows similar average weight loss between the two medications—around 15–21% for Mounjaro and approximately 15% for Wegovy. However, individual results vary significantly. Some people respond better to one medication than the other. Your personal weight loss outcome depends on your starting weight, adherence to reduced-calorie diet and activity, genetics, and individual metabolism—not on the medication alone.
How long does it take to see results after switching to Wegovy?
Wegovy is titrated from a starting dose of 0.25 mg, increasing over several weeks to find your therapeutic dose (usually 2.4 mg). Weight loss typically becomes noticeable after 4–6 weeks on a therapeutic dose, but this varies. Most people see significant results by 12–16 weeks. Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses based on clinical trial data.
What if I don't tolerate Wegovy either?
If you experience intolerable side effects on Wegovy, speak to your GP or prescriber immediately. They may suggest lowering your dose, slowing the titration schedule, or considering other weight management approaches. Liraglutide (Saxenda) is another GLP-1 option available in the UK, though it is a daily injection rather than weekly. Your prescriber can discuss alternatives suited to your individual tolerance.
Is Wegovy the same as Ozempic?
Both Wegovy and Ozempic contain the same active ingredient—semaglutide. However, Ozempic is approved for type 2 diabetes management (doses up to 2 mg) and is not licensed for weight loss in the UK. Wegovy is specifically licensed for weight management at higher doses (up to 2.4 mg). Always ask your prescriber which version you are receiving and confirm it is prescribed for weight management. ```
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