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
Is Wegovy Or Mounjaro Better For Weight Loss?
There's no single "better" option between Wegovy and Mounjaro — the right choice depends on your individual health, preferences, and how your body responds. Both are prescription-only weekly weight loss injections licensed in the UK, but they work through different mechanisms. Wegovy (semaglutide) activates one hormone pathway, while Mounjaro (tirzepatide) activates two. Clinical trials show both can help with weight loss alongside diet and exercise, though results vary significantly between individuals. Your GP or a licensed prescriber can assess which is more suitable for you after a clinical assessment.
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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.
How Wegovy And Mounjaro Work Differently
Wegovy (semaglutide) is a GLP-1 receptor agonist — it mimics a single natural hormone that reduces appetite and helps you feel fuller after eating. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, activating two hormone pathways simultaneously. This dual mechanism is what makes them different.
- Wegovy: single GLP-1 pathway; once-weekly injection; maximum dose 2.4 mg
- Mounjaro: dual GIP + GLP-1 pathway; once-weekly injection; maximum dose 15 mg
In clinical trials, Mounjaro showed slightly higher average weight loss (approximately 20.9% at the highest dose) compared to Wegovy (approximately 14.9%), though individual results vary considerably. Both work best alongside a reduced-calorie diet and increased physical activity. Try our free GLP-1 weight loss calculator to explore potential outcomes at different doses.
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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.
Side Effects, Eligibility, And Getting A Prescription
Both medications cause similar side effects — nausea, diarrhoea, and stomach pain are most common, particularly during the initial weeks. Both are prescription-only and require a clinical assessment before dispensing. UK eligibility typically includes adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea.
Access in the UK comes through two routes: NHS specialist weight management services (where waiting lists can be lengthy) or private online prescribing with a UK-licensed prescriber. There is no established clinical equivalence between doses — switching between medications must be managed by your prescriber. Your GP can advise on NHS access in your area, or you can seek a private clinical assessment to explore either option.
- 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.
Which causes fewer side effects, Wegovy or Mounjaro?
Both cause similar side effects — nausea, diarrhoea, and constipation are most common. Side effect severity varies between individuals and typically improves over time as your body adjusts. Your prescriber can discuss which might suit you better based on your medical history.
Can I switch from Wegovy to Mounjaro or vice versa?
Yes, but only under prescriber guidance. There is no official conversion chart between doses — your prescriber will assess your response and adjust accordingly. Never switch between medications without medical supervision.
Is Mounjaro always more effective than Wegovy?
Clinical trials showed Mounjaro achieved slightly higher average weight loss, but individual results vary significantly. Some people respond better to Wegovy; others respond better to Mounjaro. Your personal response cannot be predicted in advance.
How long does it take to see weight loss results?
Most people begin noticing weight loss within 4–8 weeks, though this varies. Both medications require a gradual dose titration (escalation) over weeks, and results improve as you reach higher maintenance doses. Consistency with diet and exercise is essential.
Can I get either medication on the NHS?
Both Wegovy and Mounjaro are approved by NICE for use within NHS specialist tier 3 weight management services. Access depends on your local integrated care board (ICB) and availability. Waiting lists vary significantly by region — contact your GP for referral options in your area.
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.