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
Mounjaro and Gastroparesis: What NHS Patients Should Know
Gastroparesis is a condition where the stomach empties food more slowly than normal. If you have gastroparesis and are considering Mounjaro (tirzepatide) for weight management, it's important to understand how this medication works and why it may not be suitable. Mounjaro slows gastric emptying as part of how it works, which could worsen existing gastroparesis symptoms. This guide explains what NHS patients in the UK need to know about Mounjaro, gastroparesis, and safe alternatives.
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.
Why Mounjaro May Not Be Suitable for Gastroparesis
Mounjaro is a dual GIP and GLP-1 receptor agonist that works by slowing how quickly food moves from the stomach into the small intestine. This effect is called delayed gastric emptying, and it's a key part of how Mounjaro helps reduce appetite and supports weight loss. However, if you already have gastroparesis — a condition where your stomach naturally empties too slowly — adding a medication that further delays gastric emptying could significantly worsen your symptoms.
- Mounjaro slows stomach emptying as an intended side effect (this usually reduces over time in most users, but can persist)
- Gastroparesis means your stomach already struggles to empty efficiently
- Combining both may lead to severe nausea, vomiting, abdominal pain, and nutrient absorption problems
- NHS guidance and Mounjaro safety data recommend avoiding tirzepatide if you have severe gastroparesis or gastric disorders
Your GP or specialist prescriber will ask about gastroparesis history during your clinical assessment. If you have gastroparesis, you should always disclose this before starting any weight loss medication.
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.
Alternative Weight Loss Options Through the NHS
If you have gastroparesis and need NHS support for weight management, several alternatives exist. Liraglutide (Saxenda) is a GLP-1 injection licensed in the UK for weight management and may be safer, though it also slows gastric emptying to some degree — your GP must assess this. Non-medication approaches through NHS tier 3 weight management services include structured behaviour change programmes, dietitian support, and increased physical activity planning tailored to your condition.
Your GP can refer you to a specialist weight management service where a multidisciplinary team (dietitian, psychologist, physician) can assess your individual situation, including your gastroparesis, and recommend the safest approach. Use our free BMI calculator to check your current weight category, which your GP will use as part of your eligibility assessment for NHS weight management services.
- 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 take Mounjaro if I have gastroparesis?
No, Mounjaro is not recommended if you have gastroparesis. Mounjaro slows gastric emptying as part of its mechanism, which could severely worsen gastroparesis symptoms. You should disclose any history of stomach emptying problems to your prescriber before starting any weight loss medication.
What is gastroparesis and why does it matter with Mounjaro?
Gastroparesis is a condition where the stomach empties food into the small intestine more slowly than normal, causing nausea, bloating, and pain. Since Mounjaro intentionally slows gastric emptying, combining these could be dangerous and is not recommended by prescribers.
Are there weight loss medications safer for gastroparesis?
Liraglutide (Saxenda) is another GLP-1 medication licensed in the UK for weight management, though it also affects gastric emptying. Your GP or gastroenterologist should assess whether any GLP-1 medication is appropriate for your specific situation.
How will my GP know if I have gastroparesis?
Your GP will ask detailed questions about your medical history during your initial assessment. You should inform them of any stomach emptying problems, previous diagnosis of gastroparesis, chronic nausea, vomiting, or bloating. If they suspect gastroparesis, they may refer you for tests such as a gastric emptying scan.
What are NHS alternatives to weight loss injections if I have gastroparesis?
The NHS offers tier 3 specialist weight management services including dietitian support, behaviour change programmes, and structured exercise guidance tailored to medical conditions. Your GP can refer you to these services, where a multidisciplinary team will create a safe, personalised weight management plan.
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.