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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I Can't Eat On Mounjaro — What to Do
Difficulty eating on Mounjaro is one of the most common side effects reported by UK patients. If you're struggling to eat, you're not alone — appetite suppression is how tirzepatide works, but sometimes it can feel extreme. This guide explains why this happens, when it's normal, when to contact your GP, and practical strategies to manage your nutrition while on Mounjaro treatment.
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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.
Why You Lose Your Appetite on Mounjaro
Mounjaro is a dual GIP and GLP-1 receptor agonist — it works by activating natural hormone pathways that signal fullness to your brain. When you inject tirzepatide, it actively reduces hunger signals and makes you feel satisfied after smaller meals. This appetite suppression is intentional and is how the medication helps with weight loss.
Why appetite loss happens:
- The GLP-1 pathway signals your brain that you're full — even if you've eaten very little
- Tirzepatide slows how quickly food leaves your stomach, keeping you feeling fuller for longer
- Nausea is very common, especially in the first few weeks or after a dose increase
- This effect typically improves as your body adjusts, though it varies between individuals
Most patients find their appetite naturally returns somewhat after the first 4–8 weeks as their body adapts to the medication, though the appetite-suppressing effect remains at maintenance doses.
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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.
When to Contact Your GP and How to Eat Better
If you're struggling to eat enough, prioritise nutrient-dense foods over volume. Choose protein-rich options like eggs, Greek yoghurt, and fish — even small amounts provide calories and nutrients. Bone broth, smoothies with protein powder, and soup are easier to consume when appetite is low. Keep meals small and frequent rather than three large meals.
Contact your GP urgently if:
- You cannot tolerate any food for more than a few days
- You're losing weight faster than expected (more than 1 kg per week)
- You experience severe nausea or vomiting that doesn't improve
- You feel dizzy, faint, or extremely fatigued beyond normal tiredness
- You have persistent stomach pain spreading to your back
Your prescriber may adjust your Mounjaro dose or offer additional support if appetite loss is preventing adequate nutrition.
- 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.
Is not being able to eat on Mounjaro dangerous?
Difficulty eating is common but shouldn't prevent you eating entirely. If you can manage small nutrient-dense meals (even just 600–800 kcal daily), this is usually safe. However, if you cannot eat anything for more than 24 hours, contact your GP. Severe appetite suppression may indicate your dose is too high or that you need additional support.
Will my appetite come back after a few weeks?
Yes, for most people. The most intense appetite suppression typically occurs in the first 4–8 weeks or after a dose increase. Many patients find they naturally regain some appetite after this adjustment period, though the appetite-suppressing effect of tirzepatide remains. Everyone is different — talk to your prescriber if appetite loss persists beyond 8 weeks.
What should I eat if I have no appetite on Mounjaro?
Focus on nutrient-dense, easy-to-consume foods: eggs, Greek yoghurt, protein smoothies, bone broth, soup, tinned fish, and avocado. Aim for protein with every small meal to preserve muscle during weight loss. Avoid greasy or very sweet foods, which may worsen nausea. Small, frequent meals work better than large ones.
Could loss of appetite on Mounjaro mean something else is wrong?
Appetite suppression is an expected effect of tirzepatide. However, if you also experience severe nausea, vomiting, abdominal pain, dizziness, or gradual weight management (more than 1 kg weekly), contact your GP. These could indicate pancreatitis, gallbladder issues, or dehydration — all require medical assessment.
Does Mounjaro work better if you can't eat much?
No. Extreme appetite suppression doesn't mean better weight loss results. Clinical trials showed consistent weight loss at each dose regardless of appetite level. Weight loss comes from the medication plus a sustainable calorie deficit with reduced-calorie diet and increased activity — not from eating almost nothing.
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.