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 and Gastroparesis — UK Cost and Access
Mounjaro (tirzepatide) is a prescription-only weight management injection, but it can slow how quickly food leaves your stomach — a condition called gastroparesis. This is an important consideration before starting treatment. Understanding the risks, how to access Mounjaro safely in the UK, and what it costs can help you make an informed decision alongside your GP or prescriber. If you have existing stomach problems, it's essential to discuss this before treatment begins.
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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.
Understanding Gastroparesis and Mounjaro
Gastroparesis is delayed stomach emptying — food moves more slowly from your stomach into your small intestine than normal. Mounjaro can slow gastric emptying as part of how it works, which may trigger or worsen gastroparesis symptoms in some people. Common symptoms include nausea, vomiting, abdominal pain, feeling full quickly, and bloating.
- Gastroparesis can develop during Mounjaro treatment in people without prior stomach problems
- Risk is higher in people with existing digestive conditions or diabetes
- Symptoms typically improve if Mounjaro is stopped, though this can take weeks
- Severe gastroparesis requires urgent medical attention
- Your GP should assess your digestive history before prescribing
If you experience severe, persistent stomach pain spreading to your back during Mounjaro treatment, seek immediate medical advice — this may indicate pancreatitis, a separate serious condition.
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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.
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Accessing Mounjaro in the UK — Cost and Routes
Mounjaro is available in the UK through two main routes: NHS specialist services and private prescription. NHS access is through tier 3 specialist weight management services following GP referral, though waiting lists are often lengthy and availability varies by region. Private access is through online consultations with UK-licensed prescribers, typically costing £130–£320 per month depending on dose. A prescriber will assess your medical history — including any stomach or digestive conditions — before issuing a prescription. Both routes require a clinical assessment to confirm eligibility and suitability. Use our free GLP-1 weight loss calculator to explore potential outcomes, and discuss gastroparesis risk fully with your prescriber before starting.
- 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 Mounjaro cause gastroparesis if I don't have it already?
Yes. Mounjaro can delay stomach emptying in people without prior gastroparesis. Risk is low in most people but higher in those with diabetes, existing digestive conditions, or very gradual weight management. Your prescriber should ask about your digestive history before treatment.
What's the difference between Mounjaro and Wegovy for gastroparesis risk?
Both are GLP-1-type medications that slow stomach emptying. Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist; Wegovy (semaglutide) is a GLP-1 agonist only. Gastroparesis risk exists with both, though clinical trial rates were low. Individual risk varies. Your prescriber can discuss which is safer for you.
How much does Mounjaro cost privately in the UK?
Private Mounjaro typically costs £130–£320 per month depending on the dose (2.5 mg to 15 mg). Costs vary between providers. Most private prescribers offer a consultation fee of £50–£100 (sometimes credited toward first medication cost). Always confirm pricing before starting treatment.
Can I get Mounjaro through the NHS if I have gastroparesis?
Possibly, but it depends on your circumstances. If you have symptomatic gastroparesis, you may not be suitable for Mounjaro. NHS specialist services will assess your eligibility during consultation. GP referral is the first step — discuss your digestive health openly with your GP before referral.
What should I tell a prescriber about my stomach health?
Tell them about any history of nausea, vomiting, stomach pain, bloating, constipation, or diarrhoea. Mention if you have diabetes, IBS, or other digestive conditions. Also mention any medications you take. Honesty helps your prescriber assess whether Mounjaro is safe for you and choose an appropriate starting dose.
Ready to take control of your weight loss journey?
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