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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Can You Take Mounjaro With Diverticulitis?
If you have diverticulitis or a history of digestive problems and are considering Mounjaro (tirzepatide) for weight management, it's crucial to discuss this with your GP before starting treatment. Mounjaro is a prescription-only GIP and GLP-1 receptor agonist injection that can affect how your digestive system works, which may interact with diverticulitis or increase certain risks. Your prescriber needs to know your full medical history, including any bowel conditions, to assess whether Mounjaro is safe and appropriate for you individually.
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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, Diverticulitis, and Digestive Safety
Mounjaro works by slowing gastric emptying — how quickly food moves through your stomach — and affects appetite signals. This mechanism can cause gastrointestinal side effects including nausea, constipation, and diarrhoea, which may complicate existing diverticulitis or increase flare-up risk in people with a history of the condition.
Diverticulitis occurs when small pouches (diverticula) in the colon become inflamed or infected. Factors that can trigger or worsen flare-ups include dehydration, reduced fibre intake, and digestive stress. Because Mounjaro can cause both constipation and diarrhoea — sometimes alternating — it may pose a risk for people with active or recurrent diverticulitis.
- Mounjaro may slow digestion, potentially increasing constipation risk
- Alternating bowel symptoms could stress the colon
- Dehydration from nausea or vomiting can worsen diverticulitis risk
- Your GP or gastroenterologist must assess your individual risk before prescription
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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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Wegovy vs Mounjaro: Safety Considerations for Diverticulitis
Wegovy (semaglutide), a GLP-1-only injection, works through a single mechanism compared to Mounjaro's dual GIP and GLP-1 action, but both medications carry similar digestive side effect risks. Clinical trials (SURMOUNT for Mounjaro, STEP for Wegovy) showed gastrointestinal effects in a large proportion of users, though individual tolerability varies.
Neither medication is contraindicated for diverticulitis, but both require careful prescriber assessment. The decision between Mounjaro and Wegovy — or whether either is suitable for you — depends entirely on your medical history, current symptoms, and GP guidance. Your prescriber will weigh the potential weight loss benefits against digestive risks specific to your situation. Always inform your prescriber about diverticulitis history, frequency of flare-ups, or current symptoms before starting any GLP-1 or GIP/GLP-1 medication. Use our free BMI calculator to understand your current weight status, which your GP can use as a baseline for discussing treatment options.
- 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 Mounjaro safe if I have diverticulitis?
Mounjaro is not automatically unsafe, but it requires careful assessment. Because it affects digestion and can cause constipation or diarrhoea, it may pose risks for people with active or recurrent diverticulitis. Your GP or gastroenterologist must review your full medical history and assess individual risk before prescribing. Never start Mounjaro without informing your prescriber about diverticulitis.
Can Mounjaro trigger a diverticulitis flare-up?
Possibly. Mounjaro's effects on digestion — including constipation, diarrhoea, and dehydration from nausea — could potentially trigger or worsen flare-ups in susceptible individuals. This risk is one reason prescriber assessment is essential. If you have active diverticulitis, your GP may recommend waiting until resolved before starting weight loss medication.
Is Wegovy safer than Mounjaro for diverticulitis?
Both Wegovy and Mounjaro carry similar digestive side effect risks, though Wegovy uses a single GLP-1 mechanism versus Mounjaro's dual GIP+GLP-1 action. Neither is inherently "safer" for diverticulitis — suitability depends on your individual medical profile and prescriber judgment. Only your GP can determine which, if either, is appropriate for you.
What should I tell my GP before taking Mounjaro?
Inform your GP about diverticulitis history, frequency and severity of flare-ups, current symptoms, and any medications you take. Be honest about dietary habits and any other bowel conditions. This helps your prescriber assess whether Mounjaro's digestive effects pose unacceptable risk for your situation and whether alternative weight management approaches are preferable.
Can I take Mounjaro if I've had diverticulitis in the past?
Past diverticulitis does not automatically rule out Mounjaro, but your prescriber needs to know about it. If flare-ups were infrequent and you're currently symptom-free, your GP may deem it safe. If you have recurrent episodes or active symptoms, Mounjaro may be inadvisable. This is a prescriber decision made after full assessment — never self-prescribe or skip disclosing this history.
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