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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Blood in Stool on Mounjaro — UK Cost & Access
Blood in stool (haematochezia) is a less common but serious side effect that can occur while taking Mounjaro (tirzepatide). If you experience this symptom, it requires urgent medical attention from your GP, as it may indicate pancreatitis, gastrointestinal bleeding, or other complications. This guide explains what blood in stool means on Mounjaro, how to access treatment safely in the UK, and the costs of obtaining tirzepatide through private prescription versus NHS routes. Understanding your access options helps you make informed decisions about weight management medication.
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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.
Private Mounjaro Costs by Dose in the UK
Mounjaro is available in the UK through private prescription following an online clinical assessment. Costs vary significantly by dose and provider, as each KwikPen contains four weekly injections.
- 2.5 mg dose: approximately £129–£160 per KwikPen (4 weeks)
- 5 mg dose: approximately £149–£180 per KwikPen
- 10 mg dose: approximately £189–£240 per KwikPen
- 15 mg dose: approximately £220–£280 per KwikPen (maximum)
Monthly costs range from £129 to £280 depending on your dose titration stage. Many private providers offer subscription discounts or bulk pricing. It's essential to compare providers, as prices vary. If you experience blood in stool or other serious Mounjaro side effects, you must stop and seek immediate GP advice—costs do not cover medical complications.
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.
NHS vs Private Access Routes in the UK
NHS route: Mounjaro is approved by NICE for specialist weight management services (Tier 3), but access is limited and varies by region. Your GP can refer you to a local weight management service, though waiting lists often extend months or years. If approved, Mounjaro is free on the NHS, but you cannot choose your dose escalation or timing—prescribing follows NHS protocols.
Private route: GPhC-registered online pharmacies offer tirzepatide via prescription from a UK-licensed prescriber. This requires a brief online consultation. Private access is faster (often within days) but costs apply. Both routes require clinical eligibility: BMI ≥30, or BMI 27–29.9 with weight-related health conditions. If you develop blood in stool, severe abdominal pain, or other serious Mounjaro side effects, contact your GP immediately, regardless of route.
- 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.
What should I do if I experience blood in stool while taking Mounjaro?
Blood in stool on Mounjaro is a potentially serious side effect that requires urgent medical attention. Contact your GP or NHS 111 immediately—do not wait. Possible causes include pancreatitis, gastrointestinal bleeding, or severe gastric ulceration. Stop taking Mounjaro and seek advice before your next injection. This is a medical emergency.
How much does Mounjaro cost privately in the UK per month?
Private Mounjaro costs range from approximately £129–£280 per month depending on your dose. Starting doses (2.5 mg) cost around £129–£160 per KwikPen (4 weeks), whilst maximum doses (15 mg) cost £220–£280. Prices vary between providers, so it's worth comparing. Subscription options may offer discounts.
Can I get Mounjaro free on the NHS if I experience side effects?
Yes. Mounjaro prescribed through NHS specialist weight management services is free. However, NHS access involves waiting lists and regional variation. If you're on private Mounjaro and develop serious side effects like blood in stool, your GP will still treat you through the NHS. Always inform your prescriber immediately of any concerning symptoms.
What's the difference between private Mounjaro costs and Wegovy costs in the UK?
Costs vary by provider and dose, but both GLP-1 medications (Mounjaro tirzepatide and Wegovy semaglutide) typically range from £120–£280 monthly privately. Mounjaro often costs slightly more at higher doses due to its dual GIP+GLP-1 mechanism. Prices depend on your prescriber and dose titration stage. Compare providers for the best rates, and prioritise medical safety over cost.
How do I access Mounjaro via NHS and what are the eligibility requirements?
NHS Mounjaro access requires a GP referral to your local specialist weight management service (Tier 3). Eligibility: BMI ≥30 or BMI 27–29.9 with weight-related conditions like diabetes or hypertension. South Asian, Chinese, Black African, or Black Caribbean adults may qualify at BMI 27.5+. Waiting times vary by region, sometimes several months or longer.
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.