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 If You Have IBS?
If you have irritable bowel syndrome (IBS) and are considering Mounjaro for weight management, it's important to understand how this GLP-1 and GIP receptor agonist may interact with your digestive condition. Mounjaro (tirzepatide) can affect gut function and may trigger or worsen IBS symptoms in some people. However, eligibility depends on your individual health profile and clinical assessment. This guide explains what you need to know about taking Mounjaro with IBS, how to access it in the UK, and what costs to expect.
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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 and IBS: What You Need to Know
Mounjaro works by activating GIP and GLP-1 receptors in the gut, which can significantly affect how your digestive system functions. Common Mounjaro side effects include nausea, diarrhoea, constipation, vomiting, and stomach pain — symptoms that may overlap with or worsen existing IBS.
If you have IBS, a prescriber must carefully assess whether Mounjaro is safe for you. Key considerations include:
- Type of IBS you have (constipation-predominant, diarrhoea-predominant, or mixed)
- Current IBS symptom severity and control
- Other medications you're taking for IBS management
- Whether you've had severe gastroparesis or digestion problems in the past
Some people with well-controlled IBS may tolerate Mounjaro, whilst others experience significant symptom flare-ups. A UK-licensed prescriber will review your medical history and may recommend alternative weight management approaches if Mounjaro poses too much risk. Never start Mounjaro without discussing your IBS with your prescriber — they need this information to make a safe decision.
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Accessing Mounjaro in the UK: NHS vs Private Routes
In the UK, Mounjaro can be accessed through two routes: NHS specialist services or private prescription. NHS access is through tier 3/4 specialist weight management services — you'll typically need a GP referral and assessment by a multidisciplinary team. However, NHS availability is limited and waiting times can be very long in many regions.
Private route access is faster: you complete an online consultation with a UK-licensed prescriber, and if approved, your prescription is dispensed by a GPhC-registered pharmacy. Costs typically range from £129–£320 per month depending on the dose and provider. For IBS patients, this faster route may allow you to discuss your condition directly with a prescriber before committing to ongoing treatment. Use our free BMI calculator to check your eligibility first, then consult a prescriber about IBS considerations.
- 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.
Will Mounjaro definitely make my IBS worse?
Not necessarily, but there's a significant risk. Mounjaro commonly causes diarrhoea, constipation, nausea, and stomach pain — symptoms that overlap with IBS. Some people with well-controlled IBS manage it; others experience worse flare-ups. A prescriber will assess your individual risk based on IBS type and current control.
Can I take Mounjaro if I have IBS-D (diarrhoea-predominant)?
This is higher risk. Mounjaro commonly causes diarrhoea, especially in the first weeks of treatment or when doses increase. If you have IBS-D, your prescriber may advise against Mounjaro or suggest trying a lower starting dose with close monitoring. Be honest about your symptoms during consultation.
What if I have IBS-C (constipation-predominant) instead?
Mounjaro can cause both diarrhoea and constipation — it varies between individuals. If you have IBS-C, Mounjaro's diarrhoea effect might balance your constipation, but unpredictability is risky with IBS. A prescriber needs to know your specific IBS pattern before prescribing.
How much does Mounjaro cost in the UK privately?
Private Mounjaro costs typically range from £129–£320 per month, depending on the dose (starting 2.5 mg up to 15 mg maximum). Costs vary slightly between providers. NHS access is free but availability is very limited. Check eligibility using our GLP-1 weight loss calculator, then discuss costs with a private prescriber.
What should I tell a prescriber about my IBS when applying for Mounjaro?
Be specific: tell them your IBS type (constipation, diarrhoea, or mixed), current severity, which medications control it, and any triggers. Mention any previous severe flare-ups. This information is crucial for a prescriber to decide if Mounjaro is safe for you. Honesty here protects your health.
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