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 and Diverticulitis — What UK Patients Should Know
If you're considering Mounjaro (tirzepatide) for weight management in the UK, or already taking it, understanding potential gastrointestinal risks is important. Diverticulitis is inflammation of small pouches in the colon, and there have been reports linking GLP-1 and dual GIP/GLP-1 medications to increased diverticulitis risk in clinical trials. This guide explains what NHS patients need to know, how to recognise symptoms, and when to seek medical help from your GP.
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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.
Mounjaro, GLP-1 Medications, and Diverticulitis Risk in the UK
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist licensed in the UK for weight management in adults. During the SURMOUNT clinical trials, cases of diverticulitis were reported in participants taking tirzepatide, though rates varied between dose groups. The MHRA (Medicines and Healthcare products Regulatory Agency) has reviewed this safety data and continues to monitor it closely under Black Triangle (▼) status.
Diverticulitis occurs when small pouches (diverticula) in the colon become inflamed or infected. Risk factors include age, diet low in fibre, and inflammatory conditions. Mounjaro may increase diverticulitis risk through effects on gut motility and inflammation — though the exact mechanism is still being studied. Before starting Mounjaro, your prescriber will assess your individual risk, especially if you have a history of bowel disease, recent diverticulitis, or inflammatory bowel conditions.
- Report any persistent abdominal pain, fever, or changes in bowel habits to your GP immediately
- Ensure adequate fibre intake and hydration while taking Mounjaro
- Inform your prescriber of any previous bowel or digestive problems
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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 Medical Help and NHS Next Steps
If you experience severe abdominal pain, particularly in the lower left side, accompanied by fever, nausea, or changes in bowel habits whilst taking Mounjaro, contact your GP or NHS 111 immediately. These may be signs of diverticulitis requiring urgent evaluation. Do not wait for a routine appointment — diverticulitis can develop rapidly and may require hospital assessment.
If you have a personal or family history of diverticulitis, inflammatory bowel disease, or Crohn's disease, discuss this with your GP or the prescriber before starting Mounjaro. The NHS tier 3 specialist weight management services will consider your full medical history. Use our free BMI calculator to understand your current weight status, then discuss all gastrointestinal risks openly with your healthcare team before making any decision about weight management 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.
Does Mounjaro cause diverticulitis?
Mounjaro doesn't directly cause diverticulitis, but clinical trials reported increased cases compared to placebo. The exact mechanism isn't fully understood. If you have risk factors or symptoms, discuss this with your GP before starting. Always report abdominal pain to your healthcare provider immediately.
What are the symptoms of diverticulitis I should watch for?
Symptoms include sudden severe abdominal pain (usually lower left), fever, nausea, vomiting, and constipation or diarrhoea. If you experience these whilst taking Mounjaro, contact your GP or NHS 111 urgently. Don't wait — diverticulitis requires prompt medical assessment.
Can I take Mounjaro if I've had diverticulitis before?
This depends on your individual health history and how long ago it occurred. Your GP or the NHS specialist tier 3 service will assess your specific situation. Previous diverticulitis may increase risk, so honest disclosure of your medical history is essential before starting any weight loss medication.
Is Mounjaro safe if I have Crohn's disease or inflammatory bowel disease?
Mounjaro is generally not recommended for people with active inflammatory bowel disease or Crohn's disease, as GLP-1 medications may affect gut inflammation. Always inform your prescriber of any bowel conditions. Your GP can discuss safer weight management alternatives.
What should I do if I develop diverticulitis symptoms whilst on Mounjaro?
Stop taking Mounjaro and seek immediate medical attention from your GP, A&E, or NHS 111. Diverticulitis is a medical emergency that may require antibiotics or hospital treatment. Do not delay — prompt diagnosis and treatment are essential to prevent complications.
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.