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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Does Mounjaro Increase Cancer Risk?
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK. If you're considering this medication, you may have concerns about cancer risk and side effects. This guide explains what clinical evidence shows about Mounjaro and cancer, clarifies common side effects, and helps you understand the safety profile based on available research. Always discuss any health concerns with your GP before starting any weight loss 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 Does Clinical Evidence Show About Mounjaro and Cancer?
There is currently no evidence that tirzepatide (Mounjaro) directly causes cancer in humans. The SURMOUNT clinical trials, which tested Mounjaro across thousands of participants, did not identify cancer as a side effect related to the medication itself.
However, weight loss medications undergo ongoing safety monitoring. The MHRA (UK Medicines and Healthcare Products Regulatory Agency) has placed Mounjaro under additional monitoring (Black Triangle ▼ status), meaning new safety data is reviewed regularly and adverse events are tracked closely. This is standard practice for newer medications and does not indicate a specific cancer concern—it reflects the need for continued post-market surveillance.
It's important to distinguish between: side effects caused by the medication itself, and health risks associated with obesity. Being significantly overweight increases cancer risk (linked to at least 13 types of cancer). Weight loss generally reduces cancer risk, which may be why weight loss medications are prescribed to eligible patients.
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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.
Most Common Mounjaro Side Effects — What to Expect
The most frequently reported side effects of Mounjaro affect the digestive system. In clinical trials:
- Nausea — reported by more than 1 in 10 people; often temporary and reduces over time
- Diarrhoea, vomiting, and constipation — common gastrointestinal effects
- Stomach pain — mild to moderate abdominal discomfort
- Injection site reactions — redness, bruising, or mild pain where injected
- Fatigue and dizziness — reported by some users, usually mild
- Hair loss (alopecia) — uncommon but reported; may be temporary
Most side effects are mild to moderate and often improve as your body adjusts to the medication. Use our free BMI calculator to understand your personal health baseline before starting treatment.
Serious side effects are rare but require immediate medical attention. Seek urgent care if you experience severe stomach pain spreading to your back (possible pancreatitis), serious allergic reactions (facial swelling, difficulty breathing), or changes in vision. Some patients report gallbladder problems or unusual heart rate changes.
Your prescriber will assess whether Mounjaro is safe for you based on your medical history. If you have a personal or family history of thyroid cancer, pancreatic disease, or gallbladder issues, inform your GP. Weight loss medications are prescription-only and require ongoing clinical oversight—never start without professional 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.
Has Mounjaro been linked to cancer in clinical trials?
No. Clinical trials including SURMOUNT-1 did not identify cancer as a side effect of tirzepatide. The MHRA monitors Mounjaro under additional surveillance (Black Triangle status), which is standard for newer medications but does not indicate a cancer risk.
What side effects are most common with Mounjaro?
Digestive side effects are most common—nausea, diarrhoea, vomiting, and constipation. These typically occur when starting or increasing doses and often improve over time. Injection site reactions and fatigue are also reported.
Does weight loss reduce cancer risk?
Yes. Being significantly overweight increases risk for at least 13 types of cancer. Weight loss generally reduces cancer risk, which is one reason weight loss medications are prescribed to eligible patients alongside lifestyle changes.
What serious side effects should I watch for with Mounjaro?
Seek immediate medical attention for severe stomach pain (possible pancreatitis), serious allergic reactions, changes in vision, or gallbladder symptoms. These are rare but require urgent care. Your GP can provide a full list of warning signs.
Is Mounjaro safe if I have a family history of cancer?
Having a family history of cancer does not automatically exclude you from Mounjaro, but you must inform your prescriber. They'll assess your individual risk and help decide whether this medication is appropriate for you based on your complete medical history.
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.