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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Does Your Stomach Shrink On Mounjaro — And How to Access It in the UK
Your stomach doesn't permanently shrink on Mounjaro, but the medication works by slowing how quickly food leaves your stomach and reducing your appetite, which may make you feel fuller after smaller meals. This is a temporary effect that typically reduces over time as your body adjusts. Understanding how Mounjaro works and how to access it in the UK — whether through NHS specialist services or private prescription — helps you make an informed decision about whether this medication might be suitable for your weight management journey.
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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.
How Mounjaro Affects Your Stomach and Appetite
Mounjaro (tirzepatide) works as a dual GIP and GLP-1 receptor agonist, activating two natural hormone pathways that regulate appetite and digestion. One of its effects is slowing gastric emptying — the speed at which food moves from your stomach into your small intestine. This delayed emptying creates a feeling of fullness and satisfaction, which may help you eat smaller portions and feel satisfied for longer.
This stomach-slowing effect is not permanent. Your stomach does not physically shrink. Instead, Mounjaro enhances your body's natural satiety signals, making you feel fuller sooner. Clinical trials showed that this effect is most pronounced in the early weeks of treatment and may gradually reduce as your body adapts to the medication. The primary benefit comes from appetite reduction and improved portion control, not from permanent stomach changes.
- Slowed gastric emptying — temporary effect, reduces over time
- Enhanced appetite regulation — central mechanism of action
- Smaller portion satisfaction — supports calorie deficit
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 access: Mounjaro is available through specialist tier 3 and tier 4 weight management services following NICE approval. However, access is limited and typically requires referral from your GP. Waiting lists in many regions are significantly long, sometimes 6–12 months or longer depending on your local Integrated Care Board (ICB). Your GP can advise on NHS eligibility and the referral process in your area.
Private prescription route: You can access Mounjaro through UK-registered online prescribing services. These require an online clinical assessment with a UK-licensed prescriber, who will evaluate your eligibility based on your BMI, health history, and weight-related conditions. If approved, a prescription is issued and dispensed by a GPhC-registered pharmacy. This route typically costs £129–£320 per month depending on the dose you're prescribed — higher doses cost more. The online consultation process usually takes 24–48 hours from submission to prescription.
Calculate your current BMI and weight loss potential using our free BMI calculator and GLP-1 weight loss calculator above — these can help you understand your eligibility and potential outcomes with Mounjaro before you consult a prescriber. The weight converter tool is also useful if you want to track your progress in different units (stone, kg, or lbs).
- 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.
Does Mounjaro permanently shrink your stomach?
No. Mounjaro does not permanently shrink your stomach. Instead, it slows gastric emptying and reduces appetite, making you feel fuller after smaller meals. This effect is temporary and typically reduces as your body adjusts to the medication. Your stomach remains normal in size.
How much does Mounjaro cost in the UK privately?
Private Mounjaro costs typically range from £129–£320 per month depending on your dose. The 2.5 mg starting dose is cheaper than higher maintenance doses (10 mg, 15 mg). Costs vary slightly between different UK online prescribing services. Always check the full cost including delivery before committing.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro is available through NHS specialist weight management services following NICE approval. However, access varies significantly by region and waiting lists can be very long (months to over a year). Your GP can refer you to your local tier 3 or tier 4 weight management service to discuss eligibility and timelines.
What happens to your stomach when you stop Mounjaro?
When you stop Mounjaro, the slowed gastric emptying effect reverses relatively quickly — usually within days to weeks. Your appetite regulation returns to baseline. Your stomach size does not change because it was never permanently altered. Some people experience weight regain if diet and exercise habits aren't maintained.
What is the difference between Mounjaro and Wegovy for stomach effects?
Both slow gastric emptying, but Mounjaro is a dual GIP+GLP-1 agonist whilst Wegovy is a GLP-1-only agonist. Clinical trials suggest Mounjaro may produce greater weight loss (approximately 20.9% vs 14.9%), though individual results vary. Both have similar temporary stomach-slowing effects that reduce over time.
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.