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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Mounjaro Cancer Risks — Evidence and Safety Information
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK. Like all medicines, it carries potential risks that patients should understand before starting treatment. This guide explains what current evidence shows about cancer risks associated with Mounjaro, how it compares to other weight loss medications, and what monitoring your GP recommends. All weight loss medication decisions should be made following a thorough clinical assessment with a qualified healthcare professional.
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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.
What Does the Evidence Show About Mounjaro and Cancer Risk?
Mounjaro (tirzepatide) underwent rigorous clinical trials before UK approval, with safety data carefully reviewed by the MHRA. Current evidence does not show an increased cancer risk in humans taking tirzepatide at therapeutic doses. However, like all GLP-1 and GIP receptor agonists, Mounjaro carries a Black Triangle (▼) status with the MHRA, meaning it requires additional monitoring for safety signals. Animal studies at very high doses showed thyroid tumours in rodents, but these findings do not automatically translate to human risk. Thyroid changes in humans on GLP-1 medications are being monitored closely. If you have a personal or family history of thyroid cancer (medullary thyroid carcinoma) or multiple endocrine neoplasia syndrome type 2 (MEN2), Mounjaro is contraindicated and your GP will not prescribe it. Your GP can discuss your individual risk factors during assessment and explain what monitoring may be appropriate during treatment.
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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.
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How Does Mounjaro Compare to Wegovy on Safety?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are GLP-1-based medications with similar safety profiles regarding cancer risk. Both carry Black Triangle status and require additional MHRA monitoring. Semaglutide has been used longer in diabetes care (as Ozempic), providing more long-term human safety data, though both weight management versions are relatively newer. Neither medication has demonstrated an increased cancer risk in clinical trials or real-world use data. The choice between them depends on dose titration preferences, side effect tolerance, and individual clinical factors—your prescriber will assess which suits you better. Using our GLP-1 weight loss calculator can help you understand potential outcomes with either medication, while our BMI calculator provides context for your baseline health assessment.
- 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 take long-term?
Mounjaro has been approved for long-term weight management. Safety data from clinical trials supports ongoing use alongside lifestyle changes. Black Triangle status means the MHRA monitors it closely for emerging safety signals. Your GP will review whether to continue treatment based on your individual response, side effects, and health improvements. Regular check-ups are part of safe long-term use.
What is Black Triangle status and why does Mounjaro have it?
Black Triangle (▼) status means the MHRA requires additional monitoring for safety signals. Mounjaro has this status because it is relatively new and evidence continues to accumulate. This is a standard precaution—it does not mean the medication is unsafe, but that healthcare professionals and patients should report any unexpected side effects promptly to support ongoing safety monitoring.
Should I be screened for thyroid problems before taking Mounjaro?
Your GP or prescriber will take a medical history including any thyroid conditions or family history of thyroid cancer. If you have had medullary thyroid carcinoma or MEN2 syndrome, Mounjaro is not suitable. For others, routine thyroid screening is not standard before starting, but monitoring during treatment may be recommended depending on your individual risk profile.
Can I take Mounjaro if I have a family history of cancer?
A family history of cancer does not automatically prevent Mounjaro use. However, certain cancers—specifically medullary thyroid carcinoma or conditions like MEN2—mean Mounjaro is contraindicated. Your GP will assess your specific family history and health background during the clinical assessment before prescribing.
What monitoring happens while taking Mounjaro?
Your prescriber will typically review your weight loss progress, side effects, and general health at regular intervals. Blood tests may be recommended to check metabolic markers. If you develop new symptoms—persistent stomach pain, changes in voice, or difficulty swallowing—report these to your GP immediately. Regular monitoring is part of safe, responsible weight management treatment.
Ready to take control of your weight loss journey?
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