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 5mg Mounjaro to Wegovy — What You Need to Know
If you're considering a switch from 5mg Mounjaro (tirzepatide) to Wegovy (semaglutide), you're likely wondering how they compare and whether changing medications makes sense. Both are prescription-only weight loss injections licensed in the UK, but they work slightly differently and produce different results in clinical trials. This guide explains the key differences, expected outcomes, and why any medication change requires your prescriber's input. Use our free GLP-1 weight loss calculator below to explore projected results with both options.
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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 5mg Mounjaro and Wegovy Compare: Mechanism and Clinical Trial Data
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways to regulate appetite and blood sugar. Wegovy (semaglutide) is a GLP-1-only agonist, working through a single pathway. In clinical trials, this difference shows in the results: the SURMOUNT-1 trial showed 5mg Mounjaro produced an average weight loss of approximately 15% of body weight over 72 weeks. The STEP-1 trial (Wegovy at maximum dose of 2.4mg) showed approximately 14.9% average weight loss over 68 weeks. At 5mg Mounjaro specifically, results are typically modest — many users escalate to 10mg or 15mg for greater effect. Wegovy requires escalation through 0.25mg, 0.5mg, 1mg, and 1.7mg before reaching the 2.4mg maintenance dose. Both work best alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly.
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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.
Which Medication Might Suit You — And Why Prescriber Input Matters
Deciding between Mounjaro and Wegovy depends on individual factors only your prescriber can assess. If you're currently on 5mg Mounjaro and considering Wegovy, your prescriber may suggest continuing and escalating Mounjaro (many users benefit from higher doses), or switching if you're experiencing side effects or your response has plateaued. Wegovy may suit some better due to lower starting doses or different side effect profile, though both can cause nausea and gastrointestinal effects early on. Both medications are prescription-only and require ongoing clinical assessment. Never stop one medication and start another without prescriber guidance — timing and overlap matter for safety. Calculate your potential weight loss trajectory using our GLP-1 weight loss calculator, then discuss results with your GP or weight management specialist to decide what's right for you.
- 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 5mg Mounjaro equivalent to any dose of Wegovy?
Approximate equivalence suggests 5mg Mounjaro is roughly comparable to 0.5mg or 1mg Wegovy, but these are not official conversions. Both medications work differently and require individual assessment. Your prescriber will advise the appropriate dose if you switch.
What are the key differences between Mounjaro and Wegovy mechanisms?
Mounjaro is a dual GIP and GLP-1 agonist (two hormone pathways), whilst Wegovy is GLP-1-only (single pathway). This dual mechanism is why Mounjaro sometimes produces greater average weight loss in trials, though individual response varies significantly.
Can I switch from Mounjaro to Wegovy without stopping in between?
Medication transitions must always be managed by your prescriber. Do not stop one and start another on your own — timing, overlap, and dose adjustments require clinical guidance to ensure safety and continuity of treatment.
Which medication is available on the NHS in the UK?
Both Mounjaro and Wegovy are approved for NHS specialist weight management services, but availability varies significantly by region and depends on local commissioning decisions. Waiting lists can be long. Both are also available privately through UK-licensed online prescribers.
Do Mounjaro and Wegovy have different side effects?
Both commonly cause nausea, diarrhoea, and constipation, especially at the start. Side effects often improve over time. Individual tolerance varies — some people tolerate one better than the other. Your prescriber can discuss which might suit your health profile.
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.