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
Free tracker included with every download this week
Does Mounjaro Cause Stomach Pain?
Yes, stomach pain is a recognised side effect of Mounjaro (tirzepatide), though not everyone experiences it. This injection works as a dual GIP and GLP-1 receptor agonist, which affects how your digestive system functions. Understanding what's normal, what warrants medical attention, and how to manage discomfort is essential if you're considering or currently taking this prescription-only weight management medication. Your GP or prescriber can provide personalised guidance based on your individual health.
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Calculate Your BMI Instantly
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.
How Common Is Stomach Pain With Mounjaro?
According to safety data, stomach pain is a very common side effect, affecting more than 1 in 10 people taking Mounjaro. It's one of the most frequently reported digestive symptoms alongside nausea, diarrhoea, and constipation. The pain is typically mild to moderate and tends to improve as your body adjusts to the medication during the dose titration phase — where doses increase gradually from 2.5mg up to the maintenance dose of 15mg once weekly.
- Most stomach pain occurs in the first 4 weeks after starting or increasing your dose
- Pain often settles within a few days to a week as your body adapts
- Severity may vary depending on your dose and individual tolerance
- Eating smaller, lighter meals can help reduce discomfort
If you're monitoring your weight loss journey, our free GLP-1 weight loss calculator can help you understand expected outcomes while you manage these initial side effects with your prescriber.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
When to Seek Medical Help
While mild stomach pain is expected, severe or persistent pain requires urgent medical attention. Seek immediate help from your GP or A&E if you experience severe stomach pain spreading to your back, as this may indicate pancreatitis — a rare but serious condition. Also contact your prescriber if pain lasts longer than a week, worsens despite dose adjustments, or is accompanied by vomiting you cannot manage. You should never stop taking Mounjaro without medical guidance; instead, discuss any concerning symptoms with your healthcare provider who can assess whether continuing, adjusting your dose, or pausing treatment is appropriate for your situation.
- 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?
Yes, stomach pain is a very common side effect affecting more than 1 in 10 people. It typically occurs during the first few weeks of treatment or after a dose increase, and usually improves as your body adjusts. However, individual experiences vary significantly.
What can I do to manage Mounjaro stomach pain?
Eat smaller, more frequent meals; avoid fatty or spicy foods; stay hydrated; and eat slowly. Over-the-counter antacids may help, but always check with your prescriber before taking additional medications. Your GP can advise on pain management strategies tailored to you.
How long does Mounjaro stomach pain last?
Most stomach pain resolves within a few days to a week as your body adapts. If you're increasing your dose, discomfort may briefly return, then settle again. Persistent pain beyond a week warrants discussion with your prescriber about dose adjustments.
Could stomach pain mean pancreatitis from Mounjaro?
Severe stomach pain spreading to the back may indicate pancreatitis, a rare but serious side effect. This requires urgent medical attention. Regular stomach pain is common and normal; severe pain is not. Seek immediate medical help if you're concerned.
Should I stop taking Mounjaro if I have stomach pain?
Do not stop without medical guidance. Contact your prescriber to discuss your symptoms. They can assess whether to continue, adjust your dose, pause temporarily, or switch medications. Most people manage mild pain while continuing treatment successfully.
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.