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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5mg Monjaro vs Wegovy: How Do They Compare?
Both Monjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections available in the UK, but they work differently. Monjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 agonist only. At the 5mg dose, Monjaro typically offers stronger appetite suppression, but Wegovy has longer established safety data. Both require clinical assessment before prescription, and which one suits you depends on your individual health profile and prescriber recommendation. Our free GLP-1 weight loss calculator can help you explore potential outcomes with either medication.
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Calculate Your BMI Instantly
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.
Clinical Trial Data and Mechanism Differences
The key difference lies in how each medication works. Monjaro activates two hormone pathways—GIP (glucose-dependent insulinotropic polypeptide) and GLP-1—creating a dual mechanism that may produce stronger appetite reduction and faster gastric emptying effects. In the SURMOUNT-1 clinical trial, participants on 5mg Monjaro lost approximately 15% of their body weight on average over 72 weeks, alongside reduced-calorie diet and increased physical activity.
Wegovy activates only the GLP-1 pathway. In STEP trials, participants on semaglutide achieved approximately 14.9% average weight loss at the maximum 2.4mg dose. Wegovy's single mechanism means slightly different satiety effects compared to Mounjaro's dual approach, though individual responses vary significantly.
- Starting dose: Monjaro 2.5mg vs Wegovy 0.25mg
- 5mg Monjaro context: First escalation maintenance dose, typically reached by week 5–8
- Equivalent Wegovy dose: Approximately 0.5mg (much lower dosing scale)
- Trial design: Different patient populations and study lengths affect direct comparison
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Choosing Between Them: Individual Suitability
Neither medication is universally "better"—suitability depends on your personal health factors, medical history, and how you respond. Your GP or prescriber will assess whether you're eligible for either based on BMI, weight-related health conditions, and potential side effects. Use our free BMI calculator to check where you stand against NHS thresholds. Some people experience better tolerance with Wegovy's single mechanism; others prefer Monjaro's dual action. Both require prescription and clinical assessment—neither is available over-the-counter. Availability through NHS specialist services varies by region, though both are accessible privately following online prescribing 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.
Is 5mg Monjaro stronger than Wegovy?
At the 5mg Monjaro dose, the dual GIP+GLP-1 mechanism may produce stronger appetite suppression than Wegovy 0.5mg (approximate equivalent). However, clinical trial averages showed similar overall weight loss—individual results vary significantly. Prescriber assessment determines which suits your health profile.
How long does it take to reach 5mg Monjaro?
Most people reach 5mg Monjaro by weeks 5–8, starting at 2.5mg and escalating every 4 weeks. Wegovy's escalation is slower—reaching 2.4mg takes approximately 16–20 weeks from a starting dose of 0.25mg. Timing and tolerance differ between individuals.
Which has fewer side effects, 5mg Monjaro or Wegovy?
Both cause similar side effects (nausea, diarrhoea, constipation, stomach pain). Wegovy has longer established safety data, but Monjaro is newer. Individual tolerance varies—some people experience fewer GI side effects with one over the other. Your prescriber can advise based on your health history.
Can I switch from Monjaro to Wegovy or vice versa?
Yes, switching is possible, but it must be managed by your prescriber. There's no official conversion chart—approximate equivalence exists (5mg Monjaro ≈ 0.5mg Wegovy, 10mg ≈ 1.7mg, 15mg ≈ 2.4mg), but switching requires careful clinical supervision and restart protocols.
How do I know which one I'm eligible for in the UK?
Both require BMI ≥30 or BMI 27–29.9 with weight-related health conditions (type 2 diabetes, high blood pressure, cardiovascular disease, sleep apnoea). Your GP or online prescriber will assess your eligibility. Ethnicity-adjusted thresholds apply for South Asian, Chinese, Black African, and Black Caribbean adults—lower BMI eligibility may apply.
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.