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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Wegovy and Mounjaro Dose Comparison
Wegovy and Mounjaro are both prescription-only weight loss injections licensed in the UK, but they work differently and use different dosing schedules. Wegovy (semaglutide) is a GLP-1 receptor agonist, whilst Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist — meaning it activates two hormone pathways rather than one. Understanding how their doses compare, how they're titrated, and what clinical trial data shows can help you and your GP or prescriber make an informed decision about which might be suitable for you.
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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.
Dose Schedules and Starting Points
Wegovy (semaglutide) uses a gradual titration starting at 0.25 mg and increasing every 4 weeks: 0.25 mg → 0.5 mg → 1 mg → 1.7 mg → 2.4 mg (maximum). The full titration typically takes 16–20 weeks to reach the highest dose.
Mounjaro (tirzepatide) starts at 2.5 mg and increases every 4 weeks: 2.5 mg → 5 mg → 7.5 mg → 10 mg → 12.5 mg → 15 mg (maximum). The titration is faster in absolute terms, reaching maximum dose around week 20.
Both are once-weekly injections administered as pre-filled pens — Wegovy in an auto-injection pen format and Mounjaro as the Mounjaro KwikPen. The KwikPen is designed for ease of use with a dial-up mechanism. Individual dose titration may vary — your prescriber may adjust the schedule based on your tolerance and 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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Clinical Trial Results and Mechanisms
In the SURMOUNT-1 trial, Mounjaro at 15 mg produced average weight loss of approximately 20.9% of body weight. In the STEP-1 trial, Wegovy at 2.4 mg achieved average weight loss of approximately 14.9%. However, these trials had different populations and methodologies, so direct comparison is not straightforward — individual results vary significantly.
The mechanism difference matters: Mounjaro's dual GIP plus GLP-1 action may provide additional appetite suppression compared to Wegovy's single GLP-1 pathway. Some evidence suggests Mounjaro may produce greater average weight loss, but this does not mean it is "better" — suitability depends on your individual health, tolerability, and how your body responds. Your GP or prescriber will assess which is more appropriate during a clinical assessment.
- 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 key difference between Wegovy and Mounjaro doses?
Wegovy (semaglutide) starts at 0.25 mg and titrates to 2.4 mg maximum. Mounjaro (tirzepatide) starts at 2.5 mg and titrates to 15 mg maximum. The numbers are not directly comparable — they are different medications with different mechanisms, so the dose values reflect different potencies. Both are once-weekly injections.
How long does it take to reach maximum dose on each medication?
Both typically take approximately 16–20 weeks to reach maximum dose, increasing every 4 weeks. However, this timeline is not fixed — your prescriber may adjust it based on your tolerance, side effects, and response. Some people may stay on a lower maintenance dose rather than escalating to maximum.
Which medication produces more weight loss — Wegovy or Mounjaro?
Clinical trials suggest Mounjaro may produce slightly greater average weight loss (around 20.9% vs 14.9%), but individual results vary considerably. Trial populations were different, so direct comparison has limitations. Your prescriber will discuss which is more suitable for your circumstances during a clinical assessment.
Can you switch from Wegovy to Mounjaro or vice versa?
Switching between medications is possible but must be managed by your prescriber. There is no official NHS conversion chart between Wegovy and Mounjaro doses — they are different medications. Your prescriber may adjust the starting dose and titration schedule if you switch. Never change medications without medical guidance.
Which medication has fewer side effects?
Both medications share similar common side effects: nausea, diarrhoea, vomiting, constipation, and stomach pain. Individual tolerability varies — some people tolerate one better than the other. Side effect severity often decreases over time. Your prescriber can discuss which might suit your tolerance profile during your clinical assessment.
Ready to take control of your weight loss journey?
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