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
Wegovy Pen in the UK — How It Compares to Mounjaro
Wegovy is a once-weekly prescription weight loss injection licensed in the UK that many people compare directly to Mounjaro. While both are injectable medications used for weight management, they work via different mechanisms and have distinct clinical profiles. Understanding how Wegovy differs from Mounjaro—in terms of how they work, their dosing schedules, expected results, and eligibility—can help you and your GP or prescriber decide which might be more suitable for your individual circumstances. This guide breaks down the key differences factually, so you can have an informed discussion with your healthcare provider about which option might be appropriate for you.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Mechanism, Doses, and Clinical Trial Evidence
Wegovy (semaglutide) is a GLP-1 receptor agonist only—it activates the GLP-1 hormone pathway to reduce appetite and help you feel fuller after smaller meals. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist—it activates two hormone pathways simultaneously, which may provide a different effect on appetite and weight management.
Dosing differences: Wegovy starts at 0.25 mg and escalates weekly up to a maximum of 2.4 mg once weekly. Mounjaro starts at 2.5 mg and escalates in larger increments up to 15 mg once weekly. Both require a minimum of 4 weeks at each dose before increasing.
Clinical trial outcomes: In the STEP-1 trial, Wegovy achieved average weight loss of approximately 14.9% of body weight over 68 weeks at the 2.4 mg maintenance dose. In the SURMOUNT-1 trial, Mounjaro achieved average weight loss of approximately 15% at 5 mg, 19.5% at 10 mg, and 20.9% at 15 mg over 72 weeks. Individual results vary significantly—these are population averages, not assured outcomes.
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.
Eligibility and Which Might Be Right for You
Both Wegovy and Mounjaro are prescription-only medicines in the UK, and eligibility is assessed by a prescriber on an individual basis. You may be considered for either medication if you have a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. People of South Asian, Chinese, Black African, or Black Caribbean heritage may be eligible at lower BMI thresholds (from 27.5 kg/m²).
Your prescriber will assess which medication is more suitable based on your medical history, current medications, and individual health needs. Some people respond better to one mechanism than the other—this is why the prescriber's assessment is essential. Both require accompanying lifestyle changes (reduced-calorie diet and increased physical activity) for best results. Use our free BMI calculator to check your starting point, and try our GLP-1 weight loss calculator to explore potential outcomes at different doses for both medications.
- 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 Wegovy or Mounjaro more effective for weight loss in the UK?
Clinical trials show both can support meaningful weight loss. Mounjaro showed slightly higher average weight loss percentages in trials (up to 20.9% vs ~14.9% for Wegovy), but individual results vary. Neither is "more effective" for everyone—suitability depends on your personal health profile, assessed by your prescriber. Always discuss expected outcomes realistically with your GP.
What's the difference between Wegovy's GLP-1 and Mounjaro's dual mechanism?
Wegovy activates the GLP-1 hormone pathway to reduce appetite. Mounjaro activates both GIP and GLP-1 pathways simultaneously. The dual mechanism may help some people achieve greater weight loss, but this varies individually. Your prescriber will help determine which mechanism might suit your body and health needs.
Can I switch from Wegovy to Mounjaro, or vice versa?
Switching between these medications is possible but must be managed by your prescriber. There is no official conversion chart—approximate equivalence exists (e.g. Wegovy 2.4 mg is roughly equivalent to Mounjaro 10–15 mg), but any switch requires individual assessment and careful dose adjustment to ensure safety and effectiveness.
How do I access Wegovy or Mounjaro in the UK?
Both are available through NHS specialist tier 3 weight management services (with referral from your GP, though waiting lists vary by region) or through private online consultation with a UK-licensed prescriber. Either route requires a clinical assessment to confirm eligibility and suitability. Access varies by region.
Which medication has fewer side effects—Wegovy or Mounjaro?
Both share similar common side effects: nausea, diarrhoea, vomiting, and constipation, especially during dose escalation. Individual tolerance varies—some people experience fewer side effects on one than the other. Your prescriber will monitor you and can adjust dosing if side effects are significant. Side effects often reduce as your body adjusts.
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.