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 Mounjaro Provider — What You Need to Know
If you're currently taking Mounjaro (tirzepatide) and considering switching provider or exploring alternative weight management injections like Wegovy (semaglutide), it's important to understand the clinical differences between these medications and how to make a safe transition. Both are prescription-only weight loss injections available in the UK, but they work differently and may suit different people. This guide explains what you need to know before making a change.
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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.
How Mounjaro and Wegovy Differ Clinically
Mechanism of action: Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two separate hormone pathways in your body. Wegovy is a GLP-1 receptor agonist only, activating a single pathway. This dual mechanism in Mounjaro may explain why some clinical trial participants achieved slightly higher average weight loss—approximately 20.9% of body weight on the maximum 15mg dose compared to around 14.9% for Wegovy at 2.4mg. However, individual results vary significantly.
- Mounjaro (tirzepatide): 2.5mg to 15mg weekly. Dual hormone mechanism. Average trial weight loss: 15–21% body weight.
- Wegovy (semaglutide): 0.25mg to 2.4mg weekly. Single GLP-1 mechanism. Average trial weight loss: approximately 15% body weight.
Both medications slow gastric emptying and help regulate appetite through different biological pathways. Your prescriber will assess which is more suitable based on your individual health profile, current symptoms, and treatment goals.
Clinically BackedWeight Loss
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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.
Making the Switch — What Your Prescriber Will Consider
If you're currently on Mounjaro and considering switching to Wegovy, or vice versa, you must discuss this with your prescriber—either your GP, NHS specialist, or the online prescriber handling your care. Do not stop Mounjaro and self-start another medication.
Your prescriber will evaluate: your current dose and how you've tolerated it, any side effects you're experiencing, your weight loss progress so far, any new health conditions that have developed, and whether a different mechanism might work better for you. There is no official established conversion between Mounjaro and Wegovy doses—switching requires clinical reassessment. Use our free GLP-1 weight loss calculator to understand potential outcomes at different doses, and discuss results with your prescriber before making any changes.
If you're currently on Mounjaro and considering switching to Wegovy, or vice versa, you must discuss this with your prescriber—either your GP, NHS specialist, or the online prescriber handling your care. Do not stop Mounjaro and self-start another medication.
Your prescriber will evaluate: your current dose and how you've tolerated it, any side effects you're experiencing, your weight loss progress so far, any new health conditions that have developed, and whether a different mechanism might work better for you. There is no official established conversion between Mounjaro and Wegovy doses—switching requires clinical reassessment. Use our free GLP-1 weight loss calculator to understand potential outcomes at different doses, and discuss results with your prescriber before making any changes.
- 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 medication?
No. You must discuss any switch with your prescriber first. Do not stop one medication and immediately start another. Your prescriber will manage the transition safely, which may involve stopping Mounjaro, waiting an appropriate period, and then starting Wegovy at a lower dose. This ensures your body adjusts safely between different medication types.
Is Wegovy better than Mounjaro for weight loss?
Neither is universally "better"—they work differently. In clinical trials, Mounjaro showed slightly higher average weight loss, but Wegovy works effectively for many people. Individual results vary based on your metabolism, adherence, diet, and exercise. Your prescriber will assess which suits you best based on your health history and previous medication responses.
Why would I want to switch from Mounjaro to Wegovy?
Common reasons include: persistent side effects, inadequate weight loss progress at maximum dose, cost differences, personal preference for a simpler single-mechanism medication, or if your prescriber identifies a specific health reason suggesting the other medication might work better. Always discuss concerns with your prescriber rather than switching independently.
What happens to my KwikPen prescription if I switch providers?
If you're switching from one online prescriber to another, you'll need a new clinical assessment with the new provider. They'll review your medical history, current medications, and weight loss progress before issuing a new prescription. Your KwikPen supply from your previous provider must be used up—do not mix prescriptions from different sources. Inform the new provider of your previous dose.
How long does it take to see results after switching medications?
Both Mounjaro and Wegovy typically show measurable weight loss within 4–8 weeks, though some people notice appetite changes sooner. If switching from Mounjaro to Wegovy or vice versa, it may take slightly longer as your body adjusts to the new medication. Continue your reduced-calorie diet and physical activity—medications work best alongside these lifestyle changes.
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.