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
When Was Mounjaro Released in the UK?
Mounjaro (tirzepatide) received UK regulatory approval from the MHRA in November 2023 for weight management in adults. It arrived in the UK market after Wegovy (semaglutide), which was approved in 2021. Both are now prescription-only weight loss injections available through NHS specialist services and private prescribing in the UK. Understanding the timeline and how they compare can help you discuss options with your GP.
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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 — Release Dates and Clinical Trial Data
Mounjaro arrived in the UK in 2023, making it the newer of the two major GLP-1 weight loss injections available. Wegovy (semaglutide) was approved by the MHRA in 2021, giving it approximately two years in the UK market before Mounjaro launched. The key difference is mechanism: Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways, whilst Wegovy is a GLP-1 receptor agonist only.
In clinical trials, the SURMOUNT-1 trial showed Mounjaro helped participants lose an average of 20.9% of body weight at the maximum 15 mg dose over 72 weeks. The STEP-1 trial for Wegovy showed average weight loss of 14.9% at the 2.4 mg dose over 68 weeks. Both are alongside reduced-calorie diet and increased physical activity. Individual results vary significantly depending on dose, adherence, and personal factors.
Clinically BackedWeight Loss
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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.
Which Medication Might Be Right for You?
Both Mounjaro and Wegovy are prescription-only and require a clinical assessment before being prescribed. Your prescriber will consider factors including your BMI, medical history, current medications, and personal health goals. Neither medication is automatically "better" — suitability depends on individual circumstances.
In the UK, you can access these medications through NHS specialist tier 3 weight management services (if you meet eligibility criteria and your region offers them) or through private online prescribing following an online assessment. Try our GLP-1 weight loss calculator to explore estimated outcomes at different doses, and use the BMI calculator to check your current category. Your GP can provide personalised guidance about which pathway and medication is appropriate for you.
- 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.
Did Mounjaro come to the UK before or after Wegovy?
Wegovy (semaglutide) was approved by the MHRA in 2021, whilst Mounjaro (tirzepatide) arrived in November 2023. Wegovy has been available in the UK for approximately two years longer.
What is the main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 receptor agonist (activates two hormone pathways), whilst Wegovy is a GLP-1 receptor agonist only (one pathway). This dual mechanism is why they work slightly differently in the body.
What weight loss did clinical trials show for each medication?
Mounjaro (SURMOUNT trial) showed average weight loss of 20.9% at 15 mg. Wegovy (STEP trial) showed 14.9% at 2.4 mg. Both trials included diet and exercise changes. Individual results vary considerably.
Can I get either Mounjaro or Wegovy on the NHS in the UK?
Both are available through NHS specialist tier 3 weight management services if you meet eligibility criteria (BMI ≥30 or ≥27 with weight-related health conditions) and your region offers them. Availability varies by area and waiting times can be lengthy.
How do I know which medication is suitable for me?
A prescriber must assess your medical history, current medications, BMI, and health goals. Neither is automatically better — suitability is individual. Your GP can refer you to NHS services or you can access private prescribing through an online clinical assessment.
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.