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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Pancreatitis Risk With Mounjaro vs Wegovy
Pancreatitis is a rare but serious side effect associated with GLP-1 and GIP/GLP-1 receptor agonists like Mounjaro and Wegovy. Both medications carry this risk, though it occurs in a small percentage of users. Understanding the signs, how the two medications compare, and when to seek urgent medical attention is essential for anyone taking these weight loss injections. This guide explains what you need to know about pancreatitis with Mounjaro and tirzepatide versus Wegovy in the UK context.
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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.
Clinical Evidence and Risk Comparison
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections that work through similar hormone pathways. Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1-only agonist. In the SURMOUNT-1 clinical trial for Mounjaro, pancreatitis was reported in fewer than 1% of participants across all dose levels. Similarly, in the STEP-1 trial for Wegovy, pancreatitis cases were rare. However, both medications carry a warning about pancreatitis risk in their product information. The mechanism difference between the two — Mounjaro's dual action versus Wegovy's single GLP-1 pathway — does not appear to significantly alter pancreatitis risk in clinical evidence, though individual susceptibility varies. Your prescriber will assess your personal risk factors during your clinical assessment before issuing a UK prescription.
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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.
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Symptoms and When to Seek Urgent Help
Seek emergency medical attention immediately if you experience severe, persistent stomach or abdominal pain that spreads to your back, especially when accompanied by nausea or vomiting. Other warning signs include rapid or unusual heartbeat, severe dizziness, or yellowing of the skin or eyes. Pancreatitis is a medical emergency and requires hospital assessment. Even if symptoms seem mild, contact your GP or NHS 111 if you have concerning stomach symptoms after starting Mounjaro, Wegovy, or tirzepatide injections. Your prescriber should be informed of any significant side effects. Do not assume stomach pain is just a normal adjustment side effect — have it evaluated. Early intervention is critical for safe outcomes.
- 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 likely with Mounjaro than Wegovy?
Clinical trial data suggests pancreatitis risk is similarly low for both medications, occurring in less than 1% of users. Mounjaro's dual mechanism (GIP + GLP-1) versus Wegovy's single GLP-1 pathway does not appear to increase pancreatitis risk significantly based on available evidence. Individual risk factors assessed by your prescriber matter more than the medication choice alone.
What are the early warning signs of pancreatitis?
Severe abdominal pain spreading to the back, persistent nausea or vomiting, and rapid heartbeat are key warning signs. Some people also report yellowing of skin or eyes. Seek urgent medical attention immediately if you experience these symptoms after starting a GLP-1 or GIP/GLP-1 injection.
Can I continue taking Mounjaro if I've had pancreatitis before?
No. If you have a personal or family history of pancreatitis, you should not take Mounjaro or Wegovy. This is a contraindication — your prescriber will ask about this during your clinical assessment. Always disclose full medical history before prescription.
How common is pancreatitis with these weight loss injections?
Pancreatitis is rare, occurring in less than 1% of clinical trial participants taking Mounjaro or Wegovy. However, because it is a serious condition, both medications carry warnings. Your GP can discuss your individual risk based on your health profile and whether these medications are suitable for you.
What should I do if I experience stomach pain while taking Mounjaro?
Not all stomach pain indicates pancreatitis — nausea and stomach discomfort are common side effects. However, if pain is severe, persistent, and spreads to your back, contact NHS 111 or go to A&E immediately. For mild stomach discomfort, contact your GP. Use the GLP-1 weight loss calculator on this page to review your overall suitability before starting treatment.
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