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 Long Term Effects & Cancer Risk — What the Evidence Shows
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK for adults with obesity or overweight with related health conditions. Like any medication, questions about long-term safety are important. Currently, there is no established causal link between tirzepatide and cancer in clinical trial data, though Mounjaro carries MHRA additional monitoring status (Black Triangle ▼). This guide explains what we know about long-term effects, cancer risk, and how the NHS and MHRA monitor safety for UK patients using this medication.
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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 Clinical Trials Show About Long Term Safety
Mounjaro has been studied in the SURMOUNT clinical trials, which tracked weight loss and safety outcomes over 72 weeks. These trials did not identify an increased cancer risk compared to placebo. However, it's important to understand that clinical trials have time limitations — 72 weeks is medium-term data, not decades of real-world use.
Because tirzepatide is relatively new (approved in the UK in 2023), long-term safety data spanning 10+ years does not yet exist. The MHRA has placed Mounjaro on additional monitoring (Black Triangle ▼ status), which means it will be monitored closely by healthcare professionals and patients are encouraged to report any side effects through the Yellow Card scheme. If new safety signals emerge from this ongoing monitoring, the MHRA will update guidance promptly.
Current evidence does not suggest Mounjaro causes cancer, but absolute certainty requires decades of observation across millions of users.
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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.
Cancer Risk & GLP-1 Agonists — What Research Suggests
Interestingly, some research suggests that weight loss itself may reduce certain cancer risks. Obesity is linked to 13 types of cancer (bowel, breast, endometrial, and others), so achieving a healthier weight can lower overall cancer risk. This potential benefit must be weighed against any unknown long-term medication effects.
Mounjaro is a dual GIP/GLP-1 agonist — different from single GLP-1 agonists like Wegovy (semaglutide). Animal studies have shown some GLP-1 drugs can increase C-cell tumours in rodent thyroid tissue, but this has not been replicated in humans and is not confirmed with tirzepatide specifically. Your GP can help you assess personal risk factors and whether Mounjaro is appropriate for you.
If you're concerned about long-term cancer risk and considering Mounjaro, use our free GLP-1 weight loss calculator to explore other weight management options alongside your prescriber. You can also use the BMI calculator to understand your personal health risk and discuss options with your NHS GP or specialist.
- 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.
Does Mounjaro cause cancer?
Current clinical trial data does not show a causal link between tirzepatide (Mounjaro) and cancer. However, Mounjaro has MHRA additional monitoring status because long-term safety data (10+ years) does not yet exist. Any new safety concerns are monitored via the Yellow Card scheme and will trigger guidance updates if needed.
Why does Mounjaro have a Black Triangle?
The Black Triangle (▼) symbol indicates the MHRA is conducting additional monitoring. This is standard for newer medications. It doesn't mean the drug is unsafe — it means healthcare professionals and patients should report side effects promptly so safety can be continuously assessed.
Is weight loss itself protective against cancer?
Yes, evidence suggests obesity increases risk of 13 cancer types. Losing even 5–10% of body weight may reduce cancer risk. For some patients, the cancer risk reduction from weight loss may outweigh theoretical unknown medication risks, though this is individual and requires discussion with your GP.
How long has Mounjaro been used in the UK?
Mounjaro was approved for weight management in the UK in 2023, so real-world UK experience spans roughly 2–3 years. This is medium-term data. Long-term safety information (5, 10, 20+ years) will accumulate as more patients use the medication over time.
Should I be worried about taking Mounjaro?
Mounjaro is prescription-only and prescribed only after clinical assessment by a healthcare professional who weighs benefits against risks for your individual health. If you have specific cancer concerns, discuss them with your GP or the prescriber assessing you. They can advise whether Mounjaro or an alternative is suitable for you.
Ready to take control of your weight loss journey?
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