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 Multipack vs Wegovy: What's the Difference?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections licensed in the UK, but they work differently and suit different people. Mounjaro uses a dual GIP and GLP-1 mechanism, while Wegovy is a GLP-1-only medication. This guide compares their mechanisms, clinical trial results, doses, and how eligibility works so you can understand what your prescriber might recommend. Both require clinical assessment and are used alongside lifestyle changes, not instead of them. Use our free BMI calculator to check your starting point, and explore our GLP-1 weight loss calculator to see potential outcomes at different doses.
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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 Work Differently
Mounjaro (tirzepatide) activates two hormone pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual action may help regulate appetite and fat utilisation more broadly than GLP-1 alone.
Wegovy (semaglutide) is a GLP-1 receptor agonist only—it activates the GLP-1 pathway, which signals fullness to the brain and slows stomach emptying.
In clinical trials, both showed weight loss benefits:
- Mounjaro (SURMOUNT trial): Average weight loss of 15–21% body weight depending on dose over 72 weeks
- Wegovy (STEP trial): Average weight loss of approximately 15% body weight at 68 weeks on maximum dose
These are clinical averages—individual results vary significantly. A prescriber will discuss which mechanism might suit your health profile, existing conditions, and previous treatment responses.
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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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Doses, Eligibility, and How to Access Both in the UK
Mounjaro dosing: Starts at 2.5 mg weekly, escalates over 20 weeks to a maximum of 15 mg weekly. Each KwikPen contains 4 doses (4 weeks' supply).
Wegovy dosing: Starts at 0.25 mg weekly, escalates over 16 weeks to a maximum of 2.4 mg weekly. Pre-filled pens also contain 4 doses.
Both are eligible for adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Access in the UK is through NHS specialist tier 3 services (variable waiting times and regional availability) or private online prescribing following clinical assessment. Your GP or a UK-licensed prescriber will assess which suits your health needs. Track your progress with our free progress tracker as you work towards your goals.
- 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.
What is the main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways, while Wegovy activates GLP-1 only. This difference in mechanism may affect how each medication works for different people, but individual responses vary significantly.
Which weight loss injection is more effective, Mounjaro or Wegovy?
Clinical trials showed Mounjaro with average weight loss of 15–21% and Wegovy with approximately clinically studied weight loss. However, effectiveness varies between individuals. A prescriber will recommend based on your personal health profile, not on overall trial averages. Results depend on diet, activity, genetics, and individual physiology.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between medications must be managed by your prescriber. There is no official established conversion chart—switching involves stopping one medication and starting the other with appropriate clinical supervision and dose titration to ensure safety and efficacy.
What are the starting doses for Mounjaro multipack and Wegovy?
Mounjaro starts at 2.5 mg weekly; Wegovy starts at 0.25 mg weekly. Both escalate gradually over several weeks. A multipack typically contains 4 weeks of doses. Dose increases depend on your response and tolerability, supervised by your prescriber.
Do I need NHS referral to get Mounjaro or Wegovy in the UK?
Access varies. NHS prescribing is through specialist tier 3 weight management services, requiring GP referral and varying by region. Private prescribing via online clinical assessment is also available. Both routes require a prescription from a UK-licensed prescriber following clinical evaluation of your eligibility and suitability.
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.