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 for Postpartum Weight Management
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only GLP-1 based weight management injections available in the UK, and many postpartum parents ask which might be more suitable for their situation. This guide explains how they work differently, what clinical trial evidence shows, and how your GP or prescriber determines eligibility. Individual results vary significantly, and both require a clinical assessment before prescription. Use our free GLP-1 weight loss calculator to explore potential outcomes with each medication.
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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.
How Mounjaro and Wegovy Work Differently
Wegovy (semaglutide) is a GLP-1 receptor agonist — it activates one hormone pathway that helps reduce appetite, increase feelings of fullness, and slow how quickly food leaves your stomach. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways simultaneously. This dual mechanism may offer additional appetite suppression and support for fat utilisation.
- Wegovy: Single mechanism (GLP-1 only); starting dose 0.25 mg, maximum 2.4 mg once weekly
- Mounjaro: Dual mechanism (GIP + GLP-1); starting dose 2.5 mg, maximum 15 mg once weekly
- Clinical trials: SURMOUNT-1 (Mounjaro) showed average weight loss of ~15–21% body weight; STEP-1 (Wegovy) showed average weight loss of ~14.9% body weight
- Individual results vary: Trial averages do not predict personal outcomes; many factors affect response
Both work alongside reduced-calorie diet and increased physical activity — they are not replacements for lifestyle changes. Your prescriber will discuss which mechanism may suit your health profile.
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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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Postpartum Considerations and Clinical Assessment
Postpartum weight management is individual; both Mounjaro and Wegovy require you to be at least 3 months postpartum and no longer breastfeeding before a prescriber will consider them. If you have postpartum diabetes or prediabetes, your GP may have additional preferences. Both medications require a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as hypertension, dyslipidaemia, or sleep apnoea. Use our free BMI calculator to check your current BMI and understand your starting point. Your prescriber will assess kidney function, gallbladder health, and other medical history to determine which is safest for you — there is no one-size-fits-all answer. A clinical assessment is always necessary before prescription.
- 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.
Can I take Mounjaro or Wegovy while breastfeeding?
No. Both medications should not be used during breastfeeding. You must wait until you have stopped breastfeeding and are at least 3 months postpartum before a prescriber will assess you for either medication. If breastfeeding, discuss postpartum weight management strategies with your GP.
Which causes fewer side effects — Mounjaro or Wegovy?
Both have similar common side effects: nausea, diarrhoea, constipation, and stomach pain. Individual tolerance varies greatly. Some people tolerate one better than the other, but clinical data shows comparable side effect profiles. Your prescriber will monitor your response and can adjust dose or consider switching if needed.
Will Mounjaro or Wegovy help me lose more weight than the other?
Clinical trials show Mounjaro averaged slightly higher weight loss (~15–21% vs ~14.9% for Wegovy), but individual results vary widely. Some people respond better to one mechanism than the other. Your personal outcome depends on genetics, lifestyle adherence, metabolism, and other factors — not just the medication choice.
How does the NHS KwikPen delivery work for Mounjaro?
Mounjaro comes as a pre-filled KwikPen device — each pen contains 4 weekly doses. You inject once weekly into your stomach, thigh, or upper arm. Each KwikPen is simple to use, and you dispose of it after 4 weeks. Your prescriber or nurse will show you how to inject safely.
Can my GP prescribe Mounjaro or Wegovy on the NHS postpartum?
NHS availability varies significantly by region and depends on your local integrated care board (ICB) and tier 3 specialist weight management services. You may wait months to access NHS services. Alternatively, you can access both medications through private UK-licensed prescribers via online consultation if you meet eligibility criteria.
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.