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
Which Is More Effective — Mounjaro or Wegovy?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections licensed in the UK, but they work differently and show different clinical results. Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy activates only the GLP-1 pathway. In clinical trials, Mounjaro showed slightly higher average weight loss — approximately 15–21% of body weight — compared to Wegovy's average of around 15%. However, individual results vary significantly, and the "more effective" option depends on your personal health profile, eligibility criteria, and how your body responds to treatment. Your GP or prescriber can help determine which is appropriate for you.
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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.
NHS Eligibility and NICE Guidance for Both Medications
Both Mounjaro and Wegovy are approved by NICE and available through NHS specialist tier 3 weight management services, though availability varies significantly by region and depends on your local Integrated Care Board (ICB) commissioning decisions. Eligibility for both medications is the same: adults with a BMI of 30 kg/m² or above, or BMI 27–29.9 kg/m² with a weight-related health condition such as type 2 diabetes, hypertension, or cardiovascular disease. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply.
Access through the NHS typically requires referral from your GP to a specialist weight management service, which can involve waiting lists. The STEP clinical trials demonstrated Wegovy's effectiveness, whilst Mounjaro's SURMOUNT trials showed comparable or slightly superior results. However, NHS prescribing depends on regional funding and service availability — not all areas commission both medications equally. Your prescriber will assess which option is clinically suitable based on your individual circumstances, not purely on trial data.
- NICE-approved for use in NHS specialist services
- Requires specialist assessment, not standard GP prescription
- Regional variation in availability and commissioning
- Both require a reduced-calorie diet and physical activity for effectiveness
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.
Clinical Trial Data and Practical Differences
Clinical trial averages show Mounjaro achieved approximately 15–clinically studied weight loss at maximum dose (15 mg weekly), whilst Wegovy achieved around 15% at maximum dose (2.4 mg weekly). These figures are averages from SURMOUNT-1 and STEP-1 trials respectively — individual results vary considerably. Mounjaro uses a slower dose titration (2.5 mg starting dose, increasing by 2.5 mg every 4 weeks) through the KwikPen device, whilst Wegovy starts at 0.25 mg and increases more gradually. Both are once-weekly injections.
In practice, the choice between them depends on tolerability, side effect profile, and individual response. Nausea, diarrhoea, and constipation are common with both. Use our GLP-1 weight loss calculator to estimate potential outcomes at different doses, and try our BMI calculator to track where you sit against NHS healthy weight thresholds. Your prescriber will guide you based on your medical history, current medications, and how your body tolerates the initial doses.
- 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 switch from Mounjaro to Wegovy on the NHS?
Switching between medications is possible but must be managed by your prescriber. There is no official conversion chart — your specialist will determine the appropriate Wegovy dose if switching is clinically necessary. This usually happens if you experience intolerable side effects or if the first medication doesn't achieve adequate response. NHS prescribing policies vary by region, so discuss options with your weight management service.
Which medication causes fewer side effects — Mounjaro or Wegovy?
Both have similar common side effects: nausea, diarrhoea, constipation, and stomach pain. Side effect severity and duration vary between individuals. Mounjaro's slower titration may result in more gradual nausea onset, whilst Wegovy's faster initial dose increases can cause more acute symptoms early on. Your prescriber can advise based on your tolerance and medical history.
Is Mounjaro or Wegovy available privately in the UK if I can't access it on the NHS?
Yes, both are available through private online prescribing services following a clinical assessment with a UK-licensed prescriber. Private access does not require NHS referral or specialist tier 3 services. Costs vary by provider and dose — expect approximately £129–£320 monthly depending on the medication and dose. Always use a GPhC-registered pharmacy.
What's the difference between Mounjaro's KwikPen and Wegovy's auto-injection pen?
Both are pre-filled, single-use injection devices. Mounjaro's KwikPen contains 4 doses (4 weeks supply) at a single strength per pen, so you order a new pen each month at your current dose. Wegovy pens contain 4 doses but you progress through different dose strengths (0.25 mg, 0.5 mg, 1 mg, 1.7 mg, 2.4 mg) over several months. Both are simple to use with minimal training.
How long does it take to see weight loss results with either medication?
Most people see initial weight loss within 2–4 weeks, with noticeable results by 8–12 weeks. Maximum weight loss typically occurs around 52 weeks of consistent use at an effective dose. Results depend on dose titration, adherence to reduced-calorie diet, and physical activity. Use our progress tracker to monitor your results and discuss realistic timelines with your prescriber.
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.