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 You Need to Know
If you have diverticulitis or a history of digestive problems, it's important to understand how Mounjaro might affect you before starting treatment. Mounjaro (tirzepatide) is a prescription-only weight loss injection that works by slowing how food moves through your stomach and reducing appetite. People with certain bowel conditions need to discuss this with their GP before use. This guide explains the safety considerations and what you should know about using Mounjaro if you have diverticulitis.
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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.
Mounjaro and Digestive System Effects
Mounjaro is a dual GIP and GLP-1 receptor agonist that slows gastric emptying — meaning it delays how quickly food leaves your stomach. This mechanism is what helps reduce appetite and support weight loss, but it can affect people with existing digestive conditions differently.
Diverticulitis is inflammation of small pouches (diverticula) in the colon. People with a history of diverticulitis have sensitive bowel systems that may react differently to medications that affect digestion. Mounjaro's side effects — including nausea, constipation, and stomach pain — can overlap with diverticulitis symptoms, making it harder to monitor your condition.
Key concerns for diverticulitis patients:
- Slowed digestion may aggravate symptoms in some people
- Constipation (a common Mounjaro side effect) could trigger flare-ups
- Distinguishing medication side effects from diverticulitis symptoms becomes difficult
- Individual responses vary significantly based on disease severity
Your GP or prescriber needs to know your full digestive history before assessing whether Mounjaro is suitable for you.
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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.
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NHS Guidance and How to Access Mounjaro Safely
In the UK, Mounjaro access follows two main routes: NHS specialist weight management services or private prescription through a licensed prescriber. For people with diverticulitis, NHS access is generally safer because specialists can review your full medical history and monitor you during treatment.
If accessing Mounjaro privately through an online consultation, you must disclose your diverticulitis history. A UK-licensed prescriber will assess whether the benefits outweigh risks for your specific situation. Never withhold medical information — prescribers cannot make safe decisions without complete details.
Before starting Mounjaro: Discuss with your GP whether your diverticulitis is currently active, in remission, or if you've had surgery. This context helps prescribers decide if alternative weight loss approaches might be safer. Your GP can also advise on managing both conditions together and what warning signs require urgent medical attention.
- 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.
Can I take Mounjaro if I have a history of diverticulitis?
Possibly, but only after clinical assessment by a prescriber who knows your full history. Mounjaro slows digestion, which may aggravate bowel conditions in some people. You must disclose your diverticulitis history during any online consultation or NHS assessment. Your prescriber will weigh the benefits and risks for your individual situation.
What are the warning signs I should watch for?
Seek urgent medical attention if you experience severe stomach pain spreading to your back, persistent vomiting, fever, or signs of bowel obstruction. These could indicate pancreatitis, a serious allergic reaction, or a diverticulitis flare-up. Mounjaro can cause stomach pain as a side effect, so contact your GP if symptoms are unusual or worsening.
Is Mounjaro available on the NHS for weight loss if I have diverticulitis?
Yes, if you meet NHS eligibility criteria (BMI ≥30 or BMI ≥27 with weight-related health conditions). However, NHS access is through specialist tier 3 weight management services, and your diverticulitis will be considered during assessment. Waiting lists vary by region, but NHS specialists can provide closer monitoring than private options.
What's the difference between NHS and private access to Mounjaro in the UK?
NHS access involves referral to a specialist service with ongoing medical supervision. Private access is faster but requires an online consultation with a licensed prescriber. For people with diverticulitis, NHS access is often preferable because specialists have more time to review your condition and coordinate with your GP during treatment.
What if Mounjaro triggers my diverticulitis?
If you experience symptoms suggesting a diverticulitis flare (severe cramping, fever, change in bowel habits), contact your GP immediately. You may need to pause or stop Mounjaro. Keep your GP informed throughout treatment — they can help distinguish between medication side effects and diverticulitis symptoms, and adjust your weight loss plan accordingly.
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