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 vs Wegovy Dosage: How Do They Compare?
Mounjaro (tirzepatide) and Wegovy (semaglutide) are both prescription-only weight management injections available in the UK, but they have very different dosage schedules. Mounjaro starts at 2.5 mg and escalates up to 15 mg weekly, while Wegovy begins at 0.25 mg and reaches a maximum of 2.4 mg weekly. Both are once-weekly injections, but the starting doses, escalation timelines, and maximum doses are significantly different. Understanding these differences can help you have an informed conversation with your GP or prescriber about which medication 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.
Mounjaro Dosage Schedule and Escalation
Mounjaro (tirzepatide) comes as a pre-filled KwikPen and follows this dose progression:
- Weeks 1–4: 2.5 mg once weekly (starting dose)
- Weeks 5–8: 5 mg once weekly
- Weeks 9–12: 7.5 mg once weekly
- Weeks 13–16: 10 mg once weekly
- Weeks 17–20: 12.5 mg once weekly
- Week 21+: 15 mg once weekly (maximum dose)
Each dose is held for a minimum of 4 weeks before escalating. Your prescriber will assess your response and tolerability at each stage. Clinical trials showed that participants taking 15 mg Mounjaro experienced average weight loss of approximately 21% of body weight, though individual results vary significantly. The dose titration approach allows your body to adjust gradually, which may reduce side effects like nausea.
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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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Wegovy Dosage Schedule and Escalation
Wegovy (semaglutide) uses a different escalation pattern across a longer timeframe:
- Weeks 1–4: 0.25 mg once weekly
- Weeks 5–8: 0.5 mg once weekly
- Weeks 9–12: 1 mg once weekly
- Weeks 13–16: 1.7 mg once weekly
- Week 17+: 2.4 mg once weekly (maximum dose)
Wegovy's lower starting dose reflects its single GLP-1 mechanism, compared to Mounjaro's dual GIP and GLP-1 action. In STEP clinical trials, participants on 2.4 mg Wegovy achieved average weight loss of approximately 15% of body weight over 68 weeks. Both medications require a prescription following clinical assessment to confirm eligibility. Use our GLP-1 weight loss calculator above to explore potential outcomes at different dose levels.
- 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 key difference between Mounjaro and Wegovy dosing?
Mounjaro starts at 2.5 mg and escalates to 15 mg, whilst Wegovy starts at 0.25 mg and reaches 2.4 mg. Mounjaro is a dual GIP/GLP-1 agonist, which is why its doses are higher. Both are once-weekly injections, but the escalation timelines differ slightly.
Can I switch between Mounjaro and Wegovy at equivalent doses?
These medications are not directly equivalent — there is no official conversion chart. Any switch between them must be managed by your prescriber. Approximate clinical equivalences exist (5 mg Mounjaro ≈ 0.5 mg Wegovy), but individual response varies. Your prescriber will guide dosing if you switch.
How long does it take to reach the maximum dose of each medication?
Mounjaro reaches 15 mg maximum by week 21 (approximately 5 months). Wegovy reaches 2.4 mg by week 17 (approximately 4 months). Both follow stepped escalation with minimum 4-week intervals per dose.
Which medication causes fewer side effects at lower doses?
Wegovy's very low starting dose (0.25 mg) may mean fewer initial side effects for some people. However, both medications cause nausea and gastrointestinal effects commonly during dose escalation. Side effect profiles vary significantly between individuals regardless of medication.
Are these medications available on the NHS in the UK?
NICE has approved tirzepatide (Mounjaro) and semaglutide (Wegovy) for NHS use, but availability depends on your local integrated care board and referral to tier 3 specialist weight management services. Private prescribing is also available through UK-licensed online services following clinical assessment.
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