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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Abdominal Pain on Mounjaro vs Wegovy
Stomach pain is one of the most common side effects reported with both Mounjaro and Wegovy. Both medications can cause abdominal discomfort, but the rates and mechanisms differ slightly. This guide compares what the clinical evidence shows about stomach pain with tirzepatide (Mounjaro) versus semaglutide (Wegovy), and explains when you should contact your GP. Both are prescription-only weight management injections available in the UK following clinical assessment.
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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: Mounjaro vs Wegovy Stomach Pain
Mounjaro (tirzepatide) clinical trials reported abdominal pain in approximately 26% of participants taking the highest dose (15 mg weekly). Wegovy (semaglutide) trials reported stomach pain in around 20% of participants on the maximum dose (2.4 mg weekly). Both medications slow gastric emptying — how quickly food leaves your stomach — which can cause temporary discomfort. The difference in rates may relate to their mechanisms: Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy is a GLP-1 agonist only. The dual mechanism of tirzepatide may cause slightly more gastrointestinal effects initially. However, stomach pain typically improves as your body adjusts during dose titration. Most reported cases were mild to moderate; severe pain requiring hospitalisation was uncommon in both SURMOUNT and STEP trial data.
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Managing Abdominal Discomfort and When to Seek Help
Stomach pain usually peaks in the first 1–2 weeks after starting or increasing your dose, then decreases as you adjust. To minimise discomfort: eat smaller, more frequent meals; avoid fatty or spicy foods; stay hydrated; and move gently after eating. If pain is mild, contact your prescriber or GP — do not stop your injection without guidance. Seek urgent medical attention if you experience severe, persistent abdominal pain spreading to your back, as this may indicate acute pancreatitis (rare but serious). Gallbladder problems can also cause upper stomach pain. Your GP or prescriber can assess whether continuing treatment is appropriate for you or whether switching to Wegovy might be better tolerated. Individual responses vary significantly — some people experience minimal discomfort on 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.
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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 abdominal pain more common with Mounjaro than Wegovy?
Clinical trials suggest abdominal pain is slightly more common with Mounjaro (approximately 26% at maximum dose) compared to Wegovy (approximately 20% at maximum dose). However, both medications report similar rates of severe pain. Individual tolerance varies widely, and discomfort typically improves during dose titration. Your prescriber can advise which is most suitable based on your medical history.
How long does stomach pain last when taking Mounjaro or Wegovy?
Stomach pain usually peaks within the first 1–2 weeks of starting or increasing your dose, then gradually improves as your body adjusts. Most people find discomfort settles within 4–6 weeks. If pain persists beyond this or worsens, contact your GP or prescriber — it may indicate another issue requiring investigation.
What should I do if I have severe abdominal pain on Mounjaro?
Seek urgent medical attention (call 111 or attend A&E) if you experience severe, persistent stomach pain, especially if it spreads to your back, or if you have symptoms like vomiting, fever, or yellowing of the skin. These may indicate pancreatitis or gallbladder problems. Do not wait to see your GP — get immediate medical assessment.
Can I switch from Mounjaro to Wegovy if I have stomach pain?
Yes, you can discuss switching to Wegovy with your prescriber if you're experiencing intolerable abdominal pain on Mounjaro. The approximate equivalent dose would be different (Mounjaro 10 mg ≈ Wegovy 1.7 mg; Mounjaro 15 mg ≈ Wegovy 2.4 mg), and your prescriber will manage the switch carefully. Some people tolerate Wegovy better, though results vary individually.
Are there ways to reduce abdominal pain whilst taking these medications?
Yes — eat smaller meals more frequently; avoid fatty, greasy, or spicy foods; stay well hydrated; and avoid rushing meals. Gentle walking after eating may help. Taking your injection on a consistent day and time also helps your body adjust. If these strategies don't help after 4–6 weeks, discuss alternatives with your GP or prescriber.
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