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 Pancreas Side Effects vs Wegovy
Pancreatitis is a rare but serious side effect associated with GLP-1 and GIP/GLP-1 medications like Mounjaro and Wegovy. Both prescription weight loss injections carry this risk, though it remains uncommon in clinical practice. This guide compares the pancreas safety profiles of Mounjaro (tirzepatide) and Wegovy (semaglutide), examines the clinical evidence, and explains what you need to know before starting treatment. Understanding the risks helps you and your GP make an informed decision about which medication, if any, is suitable for you.
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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.
Pancreas Risk: Clinical Evidence and Mechanism Differences
Pancreatitis — inflammation of the pancreas — is listed as a potential side effect for both Mounjaro and Wegovy in UK clinical trial data and product information. However, the actual incidence in clinical practice remains very low.
Mounjaro (SURMOUNT trials): Pancreatitis was reported in less than 1% of participants across the three main clinical trials. Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways, which theoretically could affect pancreatic function differently than single-mechanism drugs.
Wegovy (STEP trials): Similarly, pancreatitis was observed at low frequency in clinical trials. Wegovy is a GLP-1 agonist only, activating a single hormone pathway.
The difference in mechanism (dual vs single) has not been shown to produce significantly different pancreas risk in clinical data, though individual responses vary. Both medications slow gastric emptying, which may theoretically increase pancreatic stress in susceptible individuals. Your GP or prescriber can discuss your personal risk factors during assessment.
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If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
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Warning Signs and When to Seek Urgent Care
Seek immediate medical attention if you experience:
- Severe upper stomach pain radiating to the back
- Persistent nausea and vomiting that prevents eating or drinking
- Yellowing of skin or eyes (jaundice)
- Rapid or severely elevated heart rate
- Fever with abdominal pain
These symptoms may indicate pancreatitis or another serious condition requiring emergency care. Do not wait for a GP appointment — call 111 or attend A&E if symptoms are severe. If you have a history of pancreatic disease, gallstones, high triglycerides, or severe alcohol use, inform your prescriber before starting either Mounjaro or Wegovy. Individual risk factors influence suitability. Use our free GLP-1 weight loss calculator to explore projected outcomes, and discuss all risks with your healthcare provider.
- 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 pancreatitis more common with Mounjaro or Wegovy?
Clinical trial data shows pancreatitis occurs at very low rates with both medications — less than 1% of participants. No significant difference has been demonstrated between the two. Both carry the same rare risk. Individual factors like gallstones or high triglycerides increase susceptibility. Your GP will assess your personal risk during clinical assessment.
What is the difference between Mounjaro and Wegovy mechanisms regarding pancreas risk?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist; Wegovy (semaglutide) is GLP-1 only. Theoretically, dual activation might affect the pancreas differently, but clinical trials have not shown significantly higher pancreatitis risk with Mounjaro. Both slow gastric emptying, which may stress the pancreas in susceptible individuals.
Who should not take Mounjaro or Wegovy due to pancreas risk?
Avoid both medications if you have a history of pancreatitis, thyroid cancer, multiple endocrine neoplasia type 2, or severe gallbladder disease. If you have high triglycerides, previous gallstones, or alcohol use disorder, inform your prescriber — these increase pancreatitis risk. Clinical assessment determines suitability for each individual.
What should I do if I develop stomach pain while on Mounjaro or Wegovy?
Not all stomach pain indicates pancreatitis. Common side effects include mild abdominal discomfort. However, severe upper stomach pain radiating to the back, especially with persistent vomiting or jaundice, requires urgent medical attention. Call 111 or attend A&E. Do not assume it is a normal side effect — always report new or severe symptoms to a healthcare professional immediately.
How can I reduce pancreatitis risk if I take Mounjaro or Wegovy?
Take the medication exactly as prescribed — do not skip doses or increase doses without guidance. Avoid excess alcohol, which increases pancreatic inflammation risk. Stay well hydrated and follow dietary guidance from your prescriber. Attend all follow-up appointments. If you have risk factors, your GP may recommend more frequent monitoring. Report any new symptoms immediately rather than waiting for scheduled appointments.
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