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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Severe Stomach Pain on Mounjaro — What You Need to Know
Severe stomach pain is a potential serious side effect of Mounjaro (tirzepatide) that requires urgent medical attention. Unlike mild nausea or indigestion—which are very common—persistent, severe abdominal pain spreading to the back may indicate pancreatitis, a medical emergency. This guide explains what to watch for, when to contact your GP or A&E, and how the NHS approaches Mounjaro safety monitoring. If you're taking Mounjaro and experience severe stomach pain, seek immediate medical advice rather than continuing treatment.
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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.
Severe Stomach Pain on Mounjaro — NHS Safety Guidance
Severe stomach pain is not a typical side effect of Mounjaro. While nausea, constipation, indigestion, and mild stomach discomfort affect many people taking tirzepatide, severe pain spreading to the back is a warning sign of possible acute pancreatitis and requires urgent assessment.
According to MHRA guidance and the Mounjaro patient information leaflet, you should seek immediate medical help if you experience:
- Severe, persistent stomach pain that spreads to your back
- Stomach pain accompanied by vomiting
- Stomach pain with fever or signs of infection
- Pain that does not improve within 30 minutes
Pancreatitis is rare but serious. The pancreas becomes inflamed, which can affect insulin production and digestion. Do not delay—contact your GP, NHS 111, or go to A&E immediately. Your prescriber will need to assess whether you can safely continue Mounjaro. In many cases, the injection is stopped until the cause of pain is clarified.
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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.
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When to Seek Urgent NHS Care — Action Steps
If you have severe stomach pain while taking Mounjaro:
- Call NHS 111 for advice (available 24/7) — describe your symptoms and mention you're taking Mounjaro
- Go to A&E immediately if pain is very severe, you cannot keep food or fluids down, or you have signs of shock (dizziness, confusion, rapid heartbeat)
- Contact your prescriber as soon as possible — they need to know about the pain to decide on next steps
- Stop taking further doses until you've received medical assessment
Your GP or hospital doctor may order blood tests to check pancreatic enzymes (amylase and lipase), an ultrasound, or CT scan to rule out pancreatitis or gallbladder problems. Keep detailed notes of when pain started, its severity (1–10 scale), and any triggers.
- 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 stomach pain a common side effect of Mounjaro?
Mild to moderate stomach pain, indigestion, and nausea are very common with Mounjaro—affecting more than 1 in 10 people. However, severe persistent pain spreading to the back is uncommon and may signal a serious condition like pancreatitis. This requires urgent medical assessment and is not typical.
What is pancreatitis and how does Mounjaro cause it?
Pancreatitis is inflammation of the pancreas, which produces insulin and digestive enzymes. GLP-1 medications like Mounjaro can rarely trigger pancreatitis, though the exact mechanism is not fully understood. Risk is higher in people with a history of gallstones, very high triglycerides, or previous pancreatitis. Most people taking Mounjaro do not develop pancreatitis.
Can I take paracetamol or ibuprofen for Mounjaro stomach pain?
Over-the-counter painkillers may help mild indigestion or stomach discomfort. However, if you have severe pain—especially pain spreading to your back—do not rely on painkillers. Seek urgent NHS assessment instead. Pancreatitis requires medical investigation, not self-treatment. Call NHS 111 or attend A&E.
What happens if I'm diagnosed with pancreatitis while taking Mounjaro?
If pancreatitis is confirmed, Mounjaro will typically be stopped immediately. You'll receive supportive care (fluids, pain relief, dietary changes) while your pancreas recovers. Your prescriber will discuss whether you can safely restart Mounjaro later or whether an alternative weight management approach is better for you.
Does the NHS monitor Mounjaro patients for pancreatitis risk?
Mounjaro carries MHRA additional monitoring status (Black Triangle ▼), meaning all suspected serious side effects are reported to the regulator. Your prescriber should assess pancreatitis risk before you start—particularly if you have gallstone disease, a history of pancreatitis, or very high triglycerides. Use our free BMI calculator to track your baseline health metrics and discuss any concerns with your GP before starting treatment.
Ready to take control of your weight loss journey?
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