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
Free tracker included with every download this week
How to Manage Mounjaro Diarrhoea in the UK
Diarrhoea is one of the most common side effects when taking Mounjaro (tirzepatide) for weight management. Many people experience loose stools, particularly during the first few weeks or when their dose increases. The good news is that diarrhoea often improves as your body adjusts to the medication, and there are practical steps you can take to manage it. This guide explains what you can do, how to access Mounjaro in the UK, and what to expect whether you're considering NHS or private prescription routes.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
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.
Managing Diarrhoea While Taking Mounjaro
Diarrhoea typically occurs because Mounjaro slows how quickly food moves through your stomach and intestines, which can cause digestive changes. Most people find their symptoms improve within a few weeks as their body adjusts, though some experience it throughout treatment.
Practical management steps include:
- Eat smaller, more frequent meals rather than large portions
- Stay well hydrated — drink plenty of water throughout the day
- Avoid high-fat, greasy, and spicy foods, which can worsen diarrhoea
- Keep a food diary to identify triggers that affect you personally
- Increase soluble fibre gradually — oats, bananas, and rice can help
- Speak to your prescriber about over-the-counter remedies like loperamide if symptoms persist
If diarrhoea is severe or accompanied by signs of dehydration, contact your GP or the prescriber who issued your Mounjaro prescription. Calculate your BMI and weight loss projection using our free GLP-1 weight loss calculator to track your overall health progress during treatment.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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
NHS route: Mounjaro is available through specialist tier 3 weight management services following NICE approval, but availability varies significantly by region and waiting lists can be lengthy. You'll need a GP referral to access NHS specialist services.
Private route: You can access Mounjaro through a private online consultation with a UK-licensed prescriber. After a brief health assessment, if clinically appropriate, a prescription is issued and dispensed by a registered pharmacy. This route typically takes days rather than months. Costs vary by dose and provider, but private Mounjaro generally ranges from approximately £129 to £320 monthly depending on your dose strength and the prescribing service.
Whichever route you choose, diarrhoea management remains the same. Both NHS and private prescribers can advise on managing side effects. Use our free weight converter and progress tracker to monitor your weight loss journey throughout your treatment.
- 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.
How long does Mounjaro diarrhoea typically last?
For most people, diarrhoea improves within 2–4 weeks as your body adjusts to the medication. However, some people experience it longer or intermittently throughout treatment. If it persists beyond 4–6 weeks or is severely affecting your quality of life, contact your prescriber — they can advise on management strategies or dose adjustments.
Can I use over-the-counter anti-diarrhoea medication with Mounjaro?
You can use remedies like loperamide (Imodium) to help manage symptoms, but always check with your GP or prescriber first, especially if you're on other medications. They'll advise what's safe to combine with Mounjaro and whether it's appropriate for your specific situation.
Is diarrhoea a reason to stop taking Mounjaro?
Diarrhoea alone is not usually a reason to stop Mounjaro — most people find it manageable with dietary changes and patience. However, if you experience severe symptoms, signs of dehydration, or diarrhoea combined with severe stomach pain, contact your prescriber immediately. They can discuss your options, which may include dose adjustment rather than stopping.
How much does Mounjaro cost privately in the UK?
Private Mounjaro typically costs between £129 and £320 per month depending on your dose strength and the prescribing service you use. Starter doses (2.5–5 mg) are usually at the lower end, while higher maintenance doses (10–15 mg) cost more. Always confirm the full cost before starting treatment, including any consultation fees.
Can I switch from NHS to private Mounjaro if my diarrhoea isn't improving?
Yes, you can access private Mounjaro at any point. However, before switching, discuss your diarrhoea symptoms with your NHS prescriber — they may suggest dietary changes, dose adjustments, or alternative approaches. If you do switch to private, inform your new prescriber about your previous symptoms so they can manage your care appropriately from the start.
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.