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
Free tracker included with every download this week
When Does Mounjaro Peak — Comparison with Wegovy
Mounjaro (tirzepatide) typically reaches peak effectiveness between weeks 12 and 20 as your dose is gradually increased, though individual responses vary significantly. Unlike Wegovy, which uses a single GLP-1 mechanism, Mounjaro is a dual GIP and GLP-1 receptor agonist, which affects how it works and when users may notice results. Understanding the differences between these two prescription-only weight management injections can help you and your GP or prescriber make an informed decision about which might be suitable for you following a clinical assessment.
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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.
Peak Effectiveness: Mounjaro vs Wegovy Timeline
Mounjaro's dose titration schedule means peak effects come later than with Wegovy. Mounjaro starts at 2.5 mg and increases every 4 weeks (2.5 → 5 → 7.5 → 10 → 12.5 → 15 mg), with most users reaching the 10 or 15 mg maintenance dose around weeks 12–20. Clinical trials show maximum weight loss typically occurs once you've been on your maintenance dose for 8–12 weeks.
Wegovy works differently: it escalates from 0.25 mg to 2.4 mg over 16 weeks, reaching maximum dose by week 16. Peak effects are often observed by weeks 20–24 on the 2.4 mg maintenance dose. Because Wegovy uses a GLP-1 only mechanism (versus Mounjaro's dual GIP+GLP-1 action), the timeline and intensity of appetite suppression can differ between individuals.
Both medications work alongside a reduced-calorie diet and increased physical activity. Use our free GLP-1 weight loss calculator to estimate potential outcomes at different dose stages.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Individual Suitability — Prescriber Assessment
Neither Mounjaro nor Wegovy is "better" — suitability depends on your personal health profile, medical history, and how your body responds to the dual versus single hormone mechanism. Your GP or licensed prescriber will assess you individually based on your BMI, any weight-related health conditions, current medications, and previous treatment responses.
Both are prescription-only medicines available in the UK through NHS specialist weight management services (with variable waiting times and regional availability) or private online prescribing following a clinical assessment. Some people respond better to Mounjaro's dual mechanism; others prefer Wegovy's established track record. Your prescriber will discuss which is most appropriate for you. Track your progress with our free progress tracker once you begin treatment.
- 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.
When do you typically see weight loss results with Mounjaro?
Most people begin noticing changes in appetite around weeks 2–4, but meaningful weight loss typically becomes apparent by weeks 8–12. Peak weight loss usually occurs once you've reached and maintained your target dose (often 10–15 mg) for 8–12 weeks, which is usually around weeks 20–32 total. Individual timelines vary significantly.
Does Mounjaro peak faster than Wegovy?
No — if anything, Mounjaro takes slightly longer to peak due to its slower dose titration schedule. Mounjaro reaches maximum dose by week 20, while Wegovy reaches maximum by week 16. However, the dual GIP+GLP-1 mechanism may produce different appetite suppression patterns than Wegovy's GLP-1-only action.
What is the difference between Mounjaro's GIP+GLP-1 mechanism and Wegovy's GLP-1 mechanism?
Mounjaro activates two hormone pathways (GIP and GLP-1), while Wegovy activates only GLP-1. The dual mechanism may enhance appetite suppression and metabolic effects in some users, but individual responses vary. Both are evidence-based for weight management when used with lifestyle changes.
Can I switch from Mounjaro to Wegovy or vice versa?
Switches between medications are possible but must be managed by your prescriber. There is no official established conversion chart, though approximate dose equivalences exist based on clinical practice (Mounjaro 10 mg ≈ Wegovy 1.7 mg). Any change requires medical guidance and reassessment.
How long after starting Mounjaro should I expect to reach peak dose?
Full dose titration takes approximately 20 weeks to reach 15 mg (the maximum), assuming you escalate every 4 weeks without pausing. However, some people maintain lower doses (5–10 mg) if they achieve satisfactory results, and peak effectiveness for you may occur at a dose lower than the maximum.
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.