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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Stomach Pains with Mounjaro: NHS UK Information
Stomach pain and abdominal discomfort are among the most frequently reported side effects of Mounjaro (tirzepatide) in UK clinical trials. Most stomach pains are mild to moderate and tend to improve as your body adjusts to the medication. However, understanding what's normal, when to contact your GP, and how to manage these symptoms is essential for safe treatment. This guide covers NHS guidance, what to expect, and when to seek medical advice.
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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.
Common Mounjaro Stomach Pain — NHS Context
Stomach pain and discomfort occur in approximately 1 in 4 people taking Mounjaro during clinical trials, making it one of the most common side effects. Pain may feel like cramping, bloating, or general abdominal discomfort, and often accompanies other gastrointestinal symptoms such as nausea, diarrhoea, or constipation.
- During dose escalation: Stomach pain is most common in the first 4 weeks after starting Mounjaro or increasing your dose. This typically reflects your digestive system adjusting to the medication's effect on how quickly food moves through your stomach.
- Severity: Most people experience mild to moderate pain that resolves within days or weeks. Severe or persistent stomach pain is less common but requires immediate GP attention.
- Duration: For most people, stomach discomfort improves significantly after 2–4 weeks on a stable dose. Your GP can advise on managing symptoms during this adjustment period.
Our GLP-1 weight loss calculator can help you understand what to expect at each dose stage of Mounjaro treatment.
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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 Contact Your GP About Mounjaro Stomach Pain
Most stomach pain from Mounjaro is manageable, but contact your GP immediately if you experience:
- Severe, persistent stomach pain that doesn't improve after a few hours or gets worse
- Pain that spreads to your back (possible sign of pancreatitis)
- Vomiting that prevents you from keeping fluids or food down
- Severe constipation lasting more than 3 days, or sudden severe diarrhoea
- Signs of dehydration: dizziness, dark urine, extreme thirst
- Pain alongside yellowing of skin or eyes (possible gallbladder issue)
Your GP may adjust your Mounjaro dose, pause treatment, or recommend specific management strategies. Never stop taking Mounjaro without medical guidance.
- 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 normal when starting Mounjaro in the UK?
Yes. Stomach pain and abdominal discomfort are common during the first few weeks of Mounjaro treatment or when increasing doses, as your digestive system adjusts. Most people find symptoms improve within 2–4 weeks on a stable dose. However, if pain is severe or persistent, contact your GP.
What's the difference between normal Mounjaro stomach pain and something serious?
Normal pain is mild to moderate cramping or bloating that improves over days or weeks. Seek urgent GP advice if pain is severe, spreads to your back (pancreatitis risk), is accompanied by vomiting or yellowing skin, or if you show signs of dehydration.
How can I manage Mounjaro stomach pain while my body adjusts?
Eat smaller, frequent meals; stay hydrated; avoid fatty or spicy foods; and move gently after eating. Your GP or NHS dietitian can suggest specific strategies. Over-the-counter antacids may help, but check with your GP first as Mounjaro affects medication absorption.
Will my GP pause my Mounjaro if I have severe stomach pain?
Possibly. Your GP may reduce your dose, delay your next injection, or pause treatment temporarily to allow your symptoms to settle. This is a normal part of managing Mounjaro. Once symptoms improve, treatment can usually resume at a lower dose and increase more gradually.
Does stomach pain from Mounjaro happen at every dose level?
Not necessarily. Some people experience pain during dose escalation but improve once on a stable maintenance dose. Others have minimal symptoms throughout. Individual responses vary. Your NHS prescriber will monitor your tolerance and adjust your treatment plan accordingly.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.