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 Risk, and How It Compares to Wegovy
There is no established causal link between Mounjaro (tirzepatide) and cancer risk in humans based on current evidence. However, like all prescription weight loss medications, Mounjaro requires careful clinical assessment before use. This guide explains what current research shows about Mounjaro and cancer concerns, how it compares to Wegovy (semaglutide), and why individual suitability matters. Both medications are prescription-only and available in the UK following a clinical assessment from a licensed prescriber.
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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.
Clinical Evidence and Cancer Concerns
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are GLP-1 and GIP receptor agonist medications that have undergone extensive clinical trials. The SURMOUNT-1 trial for Mounjaro and the STEP trials for Wegovy monitored thousands of participants over extended periods, and neither trial identified a causal link to cancer development in human users.
Animal studies have shown dose-dependent thyroid changes in rodents at very high doses, which led to a theoretical precaution about medullary thyroid carcinoma (MTC). However, this finding has not translated to documented human cases with these medications at clinical doses. The MHRA (Medicines and Healthcare products Regulatory Authority) has reviewed this safety data and determined both medications are appropriate for use in the UK, with medullary thyroid carcinoma (MTC) listed as a contraindication for people with a personal or family history of MTC.
Any concerns about cancer risk should be discussed directly with your GP or prescribing clinician, who can assess your individual health history and suitability.
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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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Mounjaro vs Wegovy — Mechanism and Safety Profile
The key difference between these medications is their mechanism: Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 agonist only. This means Mounjaro activates two hormone pathways rather than one. Both have comparable safety profiles in clinical trials, and neither has evidence of increased cancer risk in human users at approved doses.
In the SURMOUNT-1 trial, Mounjaro helped participants lose an average of 15–21% of body weight. In the STEP trials, Wegovy supported an average weight loss of around 15%. Individual results vary significantly. Both medications are prescription-only in the UK, available through NHS specialist services or private online prescribing after clinical assessment. Your prescriber will evaluate your personal health history, medications, and suitability when deciding which medication, if any, is appropriate for you.
- 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 linked to cancer?
No causal link to cancer has been established in human clinical trials. SURMOUNT-1 and regulatory reviews by the MHRA have not identified increased cancer risk at approved doses. Medullary thyroid carcinoma is listed as a contraindication for people with personal or family history of MTC. Discuss any concerns with your GP.
How does Mounjaro compare to Wegovy for cancer risk?
Both medications have been evaluated for safety, and neither shows evidence of increased cancer risk in humans. Mounjaro is a dual GIP+GLP-1 agonist; Wegovy is GLP-1 only. Both underwent extensive clinical trials. Individual suitability depends on personal health factors, assessed by your prescriber.
What animal studies showed about these medications?
Animal studies at very high doses showed thyroid changes in rodents, leading to a theoretical precaution. This has not translated to documented cases in humans at clinical doses. The MHRA has reviewed this evidence and approved both medications for UK use with appropriate contraindications.
Do I need to worry about cancer risk if prescribed Mounjaro?
Current evidence does not support increased cancer risk at approved doses in humans. If you have a personal or family history of medullary thyroid carcinoma, inform your GP — this is a contraindication. Your prescriber will assess your individual risk factors during clinical assessment.
Can my GP help me understand the cancer risks?
Yes. Your GP or prescribing clinician can review current evidence, discuss your personal health history, and address any specific concerns about medication safety. They can also help you weigh benefits and risks in the context of your overall health. Use our free BMI calculator to understand your current health context before speaking with your prescriber.
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