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
Should You Eat Before Taking Mounjaro?
There is no specific requirement to avoid food before taking your Mounjaro (tirzepatide) injection. Unlike some medications, Mounjaro can be taken regardless of whether you have eaten or not. The timing of your meal will not affect how the injection works. However, understanding how Mounjaro affects appetite and digestion can help you manage side effects more effectively. Your prescriber will give you specific guidance based on your individual circumstances during your clinical assessment.
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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.
How Mounjaro Works With Food and Digestion
Mounjaro is a dual GIP and GLP-1 receptor agonist — it works by activating two natural hormone pathways that help regulate appetite and blood sugar. The injection itself is not affected by whether you have eaten, and food does not reduce its effectiveness. However, Mounjaro's mechanism means it slows gastric emptying — how quickly food leaves your stomach — which is why many people experience reduced appetite and feel fuller after eating smaller portions.
If you take Mounjaro and then eat a large meal, you may experience nausea or discomfort because the injection amplifies feelings of fullness. This is not dangerous, but it is why many people naturally eat less when taking Mounjaro. Some people find eating smaller, more frequent meals helps manage side effects better than eating larger meals.
- Mounjaro does not require food to activate or work
- The injection can be taken at any time of day, with or without food
- Reduced appetite is an expected effect, not a side effect to avoid
- Nausea from eating too much is temporary and typically decreases over weeks
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.
Managing Meals and Mounjaro Injections
Many people taking Mounjaro find that their relationship with food changes — they simply feel less hungry and satisfied with smaller portions. This is the intended effect. Rather than worrying about timing your meals around the injection, focus on listening to your body's hunger signals. Eat when you feel hungry, stop when you feel satisfied, and choose nutrient-dense foods to ensure you are getting adequate nutrition even though you are eating less overall.
If you experience nausea when eating, try eating more slowly, choosing bland foods temporarily, and staying hydrated. These symptoms typically improve as your body adjusts over the first few weeks on each dose. Your GP or prescriber can advise if nausea persists beyond this adjustment period. Use our GLP-1 weight loss calculator to see how Mounjaro may support your weight loss goals alongside dietary changes.
- 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 eat immediately after my Mounjaro injection?
Yes, there is no requirement to wait after your injection. You can eat whenever you feel hungry. However, many people find they feel fuller faster and eat less after taking Mounjaro, so you may not feel hungry immediately. Listen to your body's hunger signals rather than following a fixed eating schedule.
Does food affect how well Mounjaro works?
No. Mounjaro is injected into your skin and works independently of food intake. The medication's effectiveness is not reduced or increased by eating or fasting. However, Mounjaro slows stomach emptying, which means eating large meals may cause nausea — this is a normal effect that typically improves over time.
What if I feel nauseous when eating on Mounjaro?
Nausea when eating is a common early side effect that usually improves within 2–4 weeks as your body adjusts. Try eating smaller portions, eating more slowly, choosing bland foods, and staying hydrated. If nausea persists beyond the adjustment period or is severe, contact your prescriber for guidance.
Should I follow a specific diet while taking Mounjaro?
Mounjaro works best alongside a reduced-calorie diet and increased physical activity. The NHS recommends aiming for a sustainable calorie deficit of around 500 kcal per day for a loss of approximately 0.5 kg per week. Your prescriber or a dietitian can give you personalised dietary advice.
Can I take Mounjaro at any time of day?
Yes. Mounjaro is administered once weekly, and you can inject on any day that suits you — there is no requirement to inject at a particular time of day or in relation to meals. Most people choose a day that is easy to remember, like a Monday or Friday morning.
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.