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, Pancreatitis, And Wegovy — What You Need To Know
Pancreatitis is a rare but serious side effect of GLP-1 and dual GIP/GLP-1 receptor agonist medications, including Mounjaro and Wegovy. Both medications carry this risk, though it remains uncommon in clinical practice. This guide compares the pancreatitis safety profile of Mounjaro (tirzepatide) and Wegovy (semaglutide) based on clinical trial data and post-marketing safety monitoring in the UK. Understanding the signs and how these medications differ can help you and your GP make an informed decision about treatment suitability.
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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.
Pancreatitis Risk: Mounjaro Versus Wegovy Clinical Evidence
Both Mounjaro and Wegovy are prescription-only weight management injections that activate similar pathways in the body — Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy is a GLP-1 receptor agonist only. Clinical trials for both medications reported pancreatitis as a rare adverse event. In the SURMOUNT trials (Mounjaro), severe pancreatitis was reported in fewer than 1% of participants. In the STEP trials (Wegovy), pancreatitis was similarly rare. Post-marketing safety data from the UK and other countries have not identified a significant difference in pancreatitis frequency between the two medications, though individual case reports continue to be monitored by the MHRA. Both carry a black triangle warning (▼) status, meaning they remain under additional intensive monitoring for safety. Your prescriber will assess your individual risk based on your medical history, including any previous pancreatic or gallbladder conditions.
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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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Recognising Pancreatitis Symptoms And When To Seek Help
Acute pancreatitis symptoms include sudden, severe pain in the upper abdomen radiating to the back, nausea, vomiting, and sometimes fever. If you experience these symptoms whilst taking Mounjaro or Wegovy, seek urgent medical attention immediately — contact NHS 111 or attend A&E. Do not wait for a GP appointment. Pancreatitis is a medical emergency. Risk factors that may influence your suitability for either medication include a personal or family history of pancreatitis, gallstones, elevated triglycerides, or certain medications. Your GP or specialist will ask about these during your clinical assessment. If you have concerns about your pancreatic health, discuss them openly with your prescriber before starting either medication.
- 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 safer than Wegovy for pancreatitis risk?
Clinical trial data shows pancreatitis rates are rare and comparable between Mounjaro and Wegovy. Both carry similar safety profiles for this specific side effect. Your individual suitability depends on your medical history, not the medication choice alone. Your prescriber will assess your personal risk factors during clinical assessment.
What is the actual percentage risk of pancreatitis with these medications?
Pancreatitis occurred in less than 1% of participants in both SURMOUNT (Mounjaro) and STEP (Wegovy) clinical trials. In real-world UK prescribing, it remains rare. However, individual risk varies based on personal factors like prior pancreatic disease or gallstones. Always discuss your specific risk with your prescriber.
Can I take Mounjaro if I have had gallstones before?
A history of gallstones may affect your suitability for Mounjaro. Both GLP-1 and dual GIP/GLP-1 medications can increase gallbladder-related complications in some people. Your GP or specialist will review your medical history and decide whether treatment is appropriate. Do not start either medication without a full clinical assessment.
What should I do if I develop severe stomach pain whilst on Mounjaro?
Seek urgent medical attention immediately. Contact NHS 111 or attend A&E — do not wait for a routine GP appointment. Severe abdominal pain radiating to the back could indicate pancreatitis or another serious complication. Tell the healthcare team you are taking Mounjaro so they can assess you appropriately.
How does the dual GIP/GLP-1 mechanism of Mounjaro affect pancreatitis risk compared to Wegovy's single GLP-1 action?
Mounjaro's dual mechanism activates both GIP and GLP-1 pathways, whilst Wegovy activates GLP-1 only. Despite this difference, clinical trial pancreatitis rates were comparable between both medications. The additional GIP pathway in Mounjaro has not been shown to increase pancreatitis risk in published data. Individual safety depends more on your personal health profile than the mechanism used.
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