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 Week By Week: How It Compares to Wegovy
If you're researching weight loss injections in the UK, you've likely compared Mounjaro (tirzepatide) and Wegovy (semaglutide). Both are prescription-only medications that work differently and follow different week-by-week dosing schedules. Understanding how each drug escalates over time, how their mechanisms differ, and what clinical trial data shows can help you and your prescriber decide which might be suitable for you. This guide breaks down the week-by-week progression of both medications side by side.
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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.
Mounjaro and Wegovy: Week-by-Week Dose Escalation
Mounjaro (tirzepatide) starts at 2.5 mg and escalates every 4 weeks, reaching a maximum of 15 mg. The KwikPen contains four weekly injections, so each pen covers one month of treatment.
- Weeks 1–4: 2.5 mg (starting dose)
- Weeks 5–8: 5 mg (first escalation)
- Weeks 9–12: 7.5 mg
- Weeks 13–16: 10 mg
- Weeks 17–20: 12.5 mg
- Week 21+: 15 mg (maximum maintenance dose)
Wegovy (semaglutide) starts lower at 0.25 mg and escalates more gradually, reaching 2.4 mg over approximately 16–17 weeks. Each pre-filled pen contains a single weekly dose.
- Weeks 1–4: 0.25 mg
- Weeks 5–8: 0.5 mg
- Weeks 9–12: 1 mg
- Weeks 13–16: 1.7 mg
- Week 17+: 2.4 mg (maximum maintenance dose)
Both medications require at least 4 weeks on each dose before escalating. Your prescriber may adjust the schedule based on side effects or 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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Clinical Trial Data and Mechanism Differences
How they work differently: Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways that regulate appetite and blood sugar. Wegovy is a GLP-1 receptor agonist only, activating one pathway. This dual mechanism in Mounjaro may be why some clinical trial data shows slightly higher average weight loss.
SURMOUNT vs STEP trials: Mounjaro's SURMOUNT-1 trial showed average weight loss of approximately 20.9% at the maximum 15 mg dose over 72 weeks. Wegovy's STEP-1 trial showed average weight loss of approximately 14.9% at the maximum 2.4 mg dose over 68 weeks. However, individual results vary significantly, and both results were achieved alongside a reduced-calorie diet and increased physical activity. Your own weight loss will depend on many personal factors, not just which medication you take.
Which is right for you? Both Mounjaro and Wegovy require a UK prescription and clinical assessment. Your GP or a licensed prescriber will consider your medical history, current medications, BMI, and any weight-related health conditions to decide which is more suitable. Neither medication is universally "better"—what matters is which is appropriate for your individual circumstances. Use our free GLP-1 weight loss calculator to explore potential weight loss projections at different doses, and our BMI calculator to understand your current health context. A prescriber will give you personalised guidance.
- 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's the main difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) activates two hormone pathways (GIP and GLP-1), while Wegovy (semaglutide) activates one (GLP-1 only). This dual mechanism in Mounjaro may contribute to slightly higher average weight loss in clinical trials, though individual results vary. Both require a prescription and clinical assessment.
How long does it take to reach the maximum dose on each medication?
Mounjaro reaches maximum 15 mg dose by week 21 (with 4-week intervals between escalations). Wegovy reaches maximum 2.4 mg dose by week 17. Both can be used at lower maintenance doses if that's what suits you best—your prescriber decides.
Are the side effects the same for Mounjaro and Wegovy?
Both medications share common side effects including nausea, diarrhoea, vomiting, and constipation, particularly during dose escalation. Individual side effect profiles vary. Your prescriber will monitor your response and adjust if needed.
Can I switch from Wegovy to Mounjaro or vice versa?
Any switch between medications must be managed by your prescriber. Approximate dose equivalences exist (for example, Wegovy 2.4 mg is roughly equivalent to Mounjaro 15 mg), but there's no official conversion chart. Your prescriber will advise on the safest way to transition if needed.
How do I know which medication is available to me on the NHS?
Both Mounjaro and Wegovy are licensed for NHS weight management but availability varies by region and ICB. Your GP can refer you to specialist tier 3 weight management services where prescribers will assess which medication is appropriate. Waiting lists vary—some areas have very long delays.
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.