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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How to Administer Mounjaro vs Wegovy
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only, once-weekly injections licensed for weight management in the UK. While the administration process is similar for both, there are important differences in how they work, their dose ranges, and suitability for different individuals. Understanding these differences can help you and your prescriber decide which medication is right for you. Our free GLP-1 weight loss calculator and BMI calculator can help assess eligibility and potential outcomes with each option.
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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.
Mounjaro vs Wegovy: Mechanism, Doses, and Trial Data
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist—meaning it activates two natural hormone pathways that regulate appetite and blood sugar. The SURMOUNT-1 clinical trial showed average weight loss of 15% to 21% of body weight at maximum dose (15 mg once weekly) over 72 weeks, alongside diet and exercise. Doses progress from 2.5 mg up to 15 mg over approximately 20 weeks.
Wegovy (semaglutide) is a GLP-1 receptor agonist only—activating a single hormone pathway. The STEP-1 clinical trial demonstrated average weight loss of approximately 15% of body weight at maximum dose (2.4 mg once weekly) over 68 weeks. Doses progress from 0.25 mg up to 2.4 mg over approximately 16 weeks.
- Mounjaro's dual mechanism may provide enhanced appetite suppression for some individuals
- Wegovy has a longer track record and wider clinical trial data
- Individual results vary significantly—trial averages do not predict personal outcomes
- Both require a reduced-calorie diet and increased physical activity for optimal results
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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.
Administration, Eligibility, and Prescriber Decision
Both medications are delivered via pre-filled injection pens used once weekly at home. Mounjaro uses the KwikPen device; Wegovy uses an auto-injection pen. Both are injected into the stomach, thigh, or upper arm, rotating sites weekly. Storage differs slightly: Mounjaro requires refrigeration (2–8°C) when unopened; after first use, both can be kept at room temperature for up to 30 days.
Eligibility for both is the same: BMI of 30 or above, or 27 and above with weight-related health conditions such as type 2 diabetes, hypertension, or cardiovascular disease. Your prescriber will assess your medical history, current medications, and individual needs to recommend the most suitable option. Neither medication is suitable during pregnancy or whilst breastfeeding. Your GP or licensed prescriber will explain administration and monitor your progress throughout treatment.
- 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.
What is the main difference between how Mounjaro and Wegovy work?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, activating two hormone pathways. Wegovy (semaglutide) is a GLP-1 agonist only, activating one pathway. The dual mechanism in Mounjaro may provide stronger appetite suppression for some individuals, though results vary between people.
Which weight loss injection shows better results in trials?
SURMOUNT trial data for Mounjaro showed average weight loss of 15–21% of body weight at maximum dose. STEP trial data for Wegovy showed approximately 15% average weight loss. However, individual results vary significantly, and trial averages do not predict personal outcomes. Your prescriber will assess which is more suitable for you.
How do I administer Mounjaro or Wegovy at home?
Both are once-weekly injections using a pre-filled pen device. You inject into the stomach, thigh, or upper arm, rotating injection sites each week. Your prescriber will provide detailed training and written instructions. Always follow the specific guidance for your medication and never hesitate to contact your healthcare provider with questions.
Can I switch from Mounjaro to Wegovy or vice versa?
A switch between medications can only be managed by your prescriber. There is no official established conversion chart between Mounjaro and Wegovy doses. Any change in medication requires a new clinical assessment and prescription adjustment. Always consult your GP or weight management specialist before considering a switch.
Which injection is available on the NHS in the UK?
Both Mounjaro and Wegovy are approved for use within NHS specialist weight management services (tier 3/4). However, NHS access varies significantly by region and availability, with long waiting lists in many areas. Both are also available privately through GPhC-registered online pharmacies following a clinical assessment by a UK-licensed 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.