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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Mounjaro Stomach Ache — Cost and Access in the UK
Stomach ache and abdominal discomfort are among the most common side effects reported by people taking Mounjaro (tirzepatide) for weight management in the UK. If you're experiencing digestive issues with this prescription injection, understanding your treatment options—including how to access Mounjaro, what it costs, and whether NHS coverage is available—can help you decide whether to continue, adjust your dose, or explore alternatives like Wegovy. This guide explains the practical access routes and costs for Mounjaro in the UK.
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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 Cost and Access Routes in the UK
Accessing Mounjaro (tirzepatide) in the UK depends on whether you pursue NHS or private routes, each with different costs and timelines.
NHS Route: Mounjaro is available through NICE-approved specialist weight management services (tier 3 and 4). You'll need a GP referral to your local ICB (Integrated Care Board) weight management service. This is free at the point of use, but waiting times vary significantly—some areas have waiting lists of 6–18 months or longer. Eligibility requires a BMI of 30 or above, or 27 or above with weight-related health conditions (lower thresholds apply for South Asian, Chinese, Black African, and Black Caribbean adults). Once prescribed, the KwikPen device is dispensed by the NHS at no cost.
Private Route: Private prescription Mounjaro is available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber. Costs range from approximately £150–£350 per month depending on your dose (2.5 mg through 15 mg). Your first consultation typically costs £30–£50, which may be deducted from your first prescription. Private prescriptions are processed within days, not months.
Dose and Cost Relationship: Mounjaro comes in six dose strengths (2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, and 15 mg), each delivered as a once-weekly KwikPen injection. Higher doses cost more—expect approximately £20–£30 additional cost per dose level increase. Each KwikPen contains four weekly doses (one month's supply).
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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.
Managing Stomach Ache and Treatment Decisions
Stomach ache with Mounjaro often occurs in the first 4–8 weeks as your body adjusts to the medication. Most people report that discomfort improves over time, though some experience persistent gastrointestinal side effects. If stomach pain is severe or affecting your quality of life, speak to your prescriber—they may recommend dose reduction, dose pausing, or switching to an alternative like Wegovy (semaglutide), which has a different side effect profile.
When deciding between NHS and private access: NHS is free but involves waiting; private is faster but costs money. Use our free GLP-1 weight loss calculator to estimate potential weight loss outcomes at different doses—this can help you weigh whether the cost is justified by your projected results. If cost is a barrier, ask your GP about NHS eligibility or whether any local schemes offer subsidised private 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.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro (tirzepatide) is NICE-approved for NHS specialist weight management services. You need a GP referral to your local weight management tier 3 or 4 service. Eligibility requires BMI ≥30, or ≥27 with weight-related conditions (lower thresholds for certain ethnicities). Waiting lists vary by region—typically 3–18 months.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs approximately £150–£350 per month depending on dose, plus an initial consultation fee (£30–£50). Each KwikPen contains four weekly injections. Prices vary slightly between GPhC-registered online pharmacies. Higher doses (10 mg, 15 mg) cost more than lower doses (2.5 mg, 5 mg).
How long does it take to get a private Mounjaro prescription?
Private prescriptions are typically processed within 2–5 working days of your online clinical assessment. You can often receive your first KwikPen within one week. This is much faster than NHS routes, which may involve months of waiting for specialist appointments.
Is stomach ache a reason to stop Mounjaro?
Stomach ache is common but often improves within 4–8 weeks as your body adjusts. If pain is severe or persistent, speak to your prescriber—they may reduce your dose, pause treatment, or recommend switching to Wegovy or another GLP-1 medication. Never stop Mounjaro without medical guidance.
What's the difference between Mounjaro and Wegovy in terms of side effects?
Mounjaro (tirzepatide, dual GIP+GLP-1) and Wegovy (semaglutide, GLP-1 only) both cause nausea, diarrhoea, and stomach discomfort in early weeks. Individual responses vary—some people tolerate one better than the other. Your prescriber can discuss switching if side effects are problematic. Both require prescription and clinical assessment.
Ready to take control of your weight loss journey?
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