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
Does Mounjaro Cause Cancer? What the Evidence Shows
There is no evidence that Mounjaro (tirzepatide) causes cancer in humans. However, some animal studies at very high doses showed thyroid tumours in rodents — a finding that led to additional safety monitoring in the UK. Mounjaro has Black Triangle ▼ status from the MHRA, meaning it is subject to enhanced safety surveillance. This article explains the cancer concerns, what clinical evidence actually shows, and how to access this prescription medication safely through the NHS or private routes in the UK.
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.
What the Research Actually Shows About Cancer Risk
The concern about Mounjaro and cancer stems from preclinical animal studies. In laboratory rats given very high doses of tirzepatide (far exceeding human therapeutic levels), thyroid C-cell tumours developed. This finding is important — but it does not automatically mean humans face the same risk. Animal models often show effects that do not translate to people.
- SURMOUNT-1 clinical trial (the main efficacy trial in humans) found no increased cancer rates in participants taking Mounjaro compared to placebo over 72 weeks
- Real-world safety data from post-market surveillance in the US and Europe has not identified a cancer signal
- Thyroid monitoring is recommended for patients with a personal or family history of medullary thyroid carcinoma (MTC) or multiple endocrine neoplasia type 2 (MEN2)
- The MHRA Black Triangle status means healthcare providers and patients should report any unexpected side effects, helping build the safety evidence base over time
For this reason, Mounjaro is contraindicated (not suitable) for people with a personal or family history of MTC or MEN2. Your GP or prescriber will assess this during clinical evaluation.
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.
How to Access Mounjaro in the UK — NHS and Private Routes
NHS access: Available through specialist tier 3/4 weight management services following a GP referral. NICE approved tirzepatide in 2024, but regional availability varies significantly — waiting lists can be several months in many areas. You must have a BMI of 30 or above, or 27+ with weight-related health conditions (diabetes, hypertension, sleep apnoea) to qualify.
Private access: Available through GPhC-registered online pharmacies. You complete an online health questionnaire and a UK-licensed prescriber assesses your suitability. If approved, a prescription is issued and dispensed by the pharmacy. No NHS referral needed. Costs typically range from £129–£320 per month depending on dose. Once prescribed, track your progress using our free progress tracker to monitor weight loss results alongside a reduced-calorie diet and increased physical activity.
- 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 Mounjaro safe to use in the UK?
Yes. Mounjaro is approved by the MHRA and licensed for weight management in UK adults. The MHRA Black Triangle status means it is monitored closely for safety — not that it is unsafe. Clinical evidence shows no increased cancer risk in humans. Always discuss safety with your GP or prescriber before starting treatment.
What does Black Triangle status mean?
Black Triangle ▼ means the medication is subject to additional safety monitoring by the MHRA. This is standard for newer medications and indicates enhanced vigilance for rare side effects, not that the medicine is inherently unsafe. Healthcare professionals and patients are encouraged to report unexpected adverse effects.
Who cannot take Mounjaro?
Mounjaro is contraindicated for people with a personal or family history of medullary thyroid carcinoma (MTC) or multiple endocrine neoplasia type 2 (MEN2). It is also not suitable for pregnant women, children under 18, or those with severe gastroparesis. Your prescriber will assess your full medical history.
How do I know if I'm eligible for Mounjaro on the NHS?
You need a BMI of 30 kg/m² or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, hypertension, or sleep apnoea. Speak to your GP about referral to a specialist weight management service. Check your BMI using our free BMI calculator to see where you stand.
Can I switch from Wegovy to Mounjaro?
Yes, switching is possible — both are prescription-only injectables for weight management. Mounjaro is a dual GIP/GLP-1 agonist (vs Wegovy's single GLP-1 action) and uses a different dose escalation schedule. Any switch must be managed by your prescriber. Use our GLP-1 weight loss calculator to understand how the different mechanisms may affect projected outcomes.
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.