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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Diverticulitis and Mounjaro — Important Safety Information
If you have a history of diverticulitis or active diverticular disease, it's essential to understand how Mounjaro (tirzepatide) and similar weight loss medications may affect your condition. Mounjaro is a dual GIP and GLP-1 receptor agonist used for weight management in UK adults, but it slows gastric emptying—how quickly food moves through your digestive system. This effect requires careful consideration if you have inflammatory bowel conditions. Always discuss your complete medical history with your GP or prescriber before starting any weight loss medication, including Mounjaro or Wegovy. They will assess whether it's safe for your individual circumstances.
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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, Wegovy, and Gastrointestinal Health
Mounjaro (tirzepatide) is a prescription-only injection that works by activating two hormone pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1. Wegovy (semaglutide) activates GLP-1 only. Both medications slow how quickly food leaves your stomach—this is how they help reduce appetite and support weight loss. For people with a history of diverticulitis, this delayed gastric emptying could potentially trigger inflammation if not carefully managed. Diverticulitis involves inflammation of small pouches (diverticula) in the colon, and reduced digestive movement may increase pressure in affected areas. Clinical trials show Mounjaro produces average weight loss of 15–21% of body weight, while Wegovy produces approximately 15% in trials—but individual results vary significantly. Both require a reduced-calorie diet and increased physical activity alongside the medication. Your GP needs to know about any history of gastrointestinal inflammation before prescribing either medication.
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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.
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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Individual Assessment and Prescriber Decision
Whether Mounjaro or Wegovy is suitable if you have diverticulitis is a decision only your prescriber can make after reviewing your full medical history and current health status. They may recommend Wegovy (GLP-1 only) over Mounjaro (dual GIP+GLP-1) if they feel the lower physiological impact is safer for your digestive health, though this is not a rule—it's a clinical judgment. Some patients with well-controlled or resolved diverticulitis may tolerate weight loss medications safely, whilst others may not be suitable candidates. Never start Mounjaro or Wegovy without a clinical assessment. Both are prescription-only and available through NHS specialist weight management services or private prescribing following an online consultation. Your prescriber will weigh the benefits of weight loss (which may reduce strain on your digestive system long-term through improved health outcomes) against the short-term risks of medication-induced delayed gastric emptying.
- 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 diverticulitis?
Mounjaro may not be suitable if you have active diverticulitis or a recent history of it. Your GP or prescriber must assess your individual case. They will consider the severity and timing of your condition, your current symptoms, and whether the benefits of weight loss outweigh digestive risks. Never start Mounjaro without consulting your prescriber about your gastrointestinal history.
Is Wegovy safer than Mounjaro for diverticulitis?
Wegovy (GLP-1 only) may be considered safer than Mounjaro (dual GIP+GLP-1) for some people with diverticulitis because it has a single mechanism of action rather than dual. However, both slow gastric emptying. Your prescriber will decide which, if either, is appropriate based on your medical history. Neither is necessarily "safer"—it depends on your individual circumstances.
What are the main differences between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 receptor agonist with doses up to 15mg weekly. Wegovy is a GLP-1 agonist only, with doses up to 2.4mg weekly. In clinical trials (SURMOUNT and STEP), Mounjaro showed average weight loss of 15–21%, whilst Wegovy showed approximately 15%. Both require lifestyle changes alongside medication. Both slow gastric emptying, which is why GI history matters.
How do I know if I'm eligible for Mounjaro or Wegovy in the UK?
You're typically eligible if you have a BMI of 30 or above, or 27–29.9 with weight-related health conditions. For South Asian, Chinese, Black African, or Black Caribbean adults, lower thresholds apply. A prescriber will assess you during a consultation. Your medical history—including any history of diverticulitis—will be reviewed before prescription.
Should I lose weight if I have diverticulitis?
Weight loss can reduce overall strain on your digestive system and lower risks of type 2 diabetes, cardiovascular disease, and other obesity-linked conditions. However, the method matters. Discuss with your GP whether weight loss injections are safe for you, or whether a slower, diet-based approach might be safer. Safe weight loss is typically 0.5–1kg per week.
Ready to take control of your weight loss journey?
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