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
How Long Has Mounjaro Been Tested in Clinical Trials?
Mounjaro (tirzepatide) has undergone rigorous clinical testing for over three years before UK approval. The SURMOUNT trials, which began in 2021, provided the evidence that led to MHRA authorisation in 2023. Understanding the testing timeline and evidence behind Mounjaro helps you make informed decisions about weight management options. Our GLP-1 weight loss calculator can help you explore potential outcomes based on clinical data, whilst your GP can assess whether this prescription-only medicine is right for your individual circumstances.
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.
Clinical Testing Timeline and SURMOUNT Trial Data
Mounjaro's development and testing pathway:
- Early development began in 2018–2019 with laboratory and animal testing
- Phase 1 clinical trials (2019–2020) assessed safety and initial dosing in healthy volunteers
- Phase 2 trials (2020–2021) tested efficacy in people with overweight and obesity
- Phase 3 SURMOUNT trials (2021–2023) involved over 4,500 participants across multiple studies
- MHRA (UK medicines regulator) granted approval in November 2023 following comprehensive data review
The SURMOUNT-1 trial, the largest study, ran for 72 weeks and showed that participants taking tirzepatide at maximum dose (15 mg once weekly) lost an average of 20.9% of their body weight. This robust evidence underpins NHS and private prescribing decisions in the UK. The dual GIP and GLP-1 mechanism distinguishes Mounjaro from other weight loss medications like semaglutide (Wegovy), which targets only the GLP-1 pathway.
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.
NHS Approval and Ongoing Safety Monitoring
Following MHRA approval, Mounjaro received a Black Triangle (▼) designation, meaning it remains under additional monitoring for safety data. This is standard for new weight management medications and does not indicate a safety concern — it simply means the MHRA continues to collect and review reports. NICE (National Institute for Health and Care Excellence) has endorsed tirzepatide for use within NHS specialist weight management services, though access varies by region and availability. Your GP can assess whether referral to a tier 3 specialist weight management service is appropriate for you. Use our free BMI calculator to understand your current status and discuss NHS options with your healthcare provider.
- 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.
When was Mounjaro first approved in the UK?
Mounjaro (tirzepatide) was approved by the MHRA in November 2023. Clinical testing through the SURMOUNT trials ran from 2021 to 2023, providing evidence of safety and efficacy in weight management before regulatory approval.
How many people were involved in Mounjaro clinical trials?
Over 4,500 participants took part in the Phase 3 SURMOUNT trials, with the largest study (SURMOUNT-1) involving approximately 2,500 people. This large sample size strengthens the reliability of the results and safety data.
Is Mounjaro still being monitored for safety after NHS approval?
Yes. Mounjaro carries a Black Triangle (▼) designation, meaning it remains under additional MHRA monitoring. This is routine for newer weight loss medications and allows ongoing safety data collection — it does not indicate safety concerns.
How does Mounjaro's testing compare to Wegovy?
Both underwent Phase 3 trials lasting 68–72 weeks. Mounjaro's SURMOUNT trials showed average weight loss of 15–21% at maximum dose, while Wegovy's STEP trials showed approximately 14.9% average loss. Testing timelines were similar, with both now approved and monitored in the UK.
Can I access Mounjaro through the NHS based on clinical trial evidence?
Yes. NHS approval is based on SURMOUNT trial data showing safety and efficacy. Access is through specialist tier 3 weight management services following GP referral. Availability varies by region. A prescriber will assess whether Mounjaro is appropriate for you based on your individual health.
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.