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
How Do You Feel On Mounjaro?
When you start Mounjaro (tirzepatide), you may experience a range of physical and appetite-related changes as your body adjusts to this dual GIP and GLP-1 receptor agonist. Most people report feeling fuller more quickly, reduced food cravings, and changes in digestion. Understanding what to expect can help you prepare for your weight management journey and recognise normal adjustment symptoms. Individual experiences vary significantly depending on your dose, metabolism, and overall health.
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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.
Common Feelings and Physical Changes on Mounjaro
Most people on Mounjaro report experiencing reduced appetite within the first few weeks, often noticing they feel full after eating much smaller portions than usual. You may also experience reduced interest in food and changes in taste preferences — some users report finding previously favourite foods less appealing. Common physical sensations include mild nausea (especially in the first 2–4 weeks), which often improves as your body adjusts to each dose. Many people feel less bloated and experience improved digestion after several weeks of treatment. Some users describe a sense of control around food for the first time, with fewer cravings and less urge to snack between meals. Energy levels vary — some feel more energised due to better food choices, whilst others report temporary fatigue during dose escalation. These feelings typically stabilise within 4–8 weeks at each new dose level.
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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.
Side Effects and How They Feel
Gastrointestinal side effects are very common on Mounjaro, particularly in the first month. Nausea affects many users and often feels worse on an empty stomach or after eating rich foods. Constipation and diarrhoea are frequent — your digestive system is adjusting to how Mounjaro slows food movement through your stomach. Stomach discomfort may feel like mild cramping or bloating, usually manageable with dietary adjustments. Most side effects improve significantly within 4 weeks, though some people experience mild ongoing nausea at higher doses. Injection site reactions (redness, bruising, or mild soreness) are usually minor and fade quickly. If you experience severe, persistent stomach pain, contact your GP immediately — this could indicate pancreatitis, though it is rare.
- 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.
Will I feel hungry at all on Mounjaro?
Most people on Mounjaro experience significantly reduced hunger, but this varies by individual and dose. You may still feel physical hunger sensations, but the psychological urge to eat is usually much weaker. Some users report feeling satisfied with small meals and not thinking about food between meals — a major change from their previous experience.
How long does it take to feel the effects of Mounjaro?
Many people notice reduced appetite within 3–5 days of their first 2.5 mg dose, though some take 1–2 weeks. Effects become more pronounced as you move through dose escalation — typically stronger at 5 mg, 10 mg, and 15 mg. Peak effects usually occur 4–8 weeks after reaching your target maintenance dose.
When will nausea stop on Mounjaro?
Nausea is most common in the first 2–4 weeks and often improves significantly by week 4–8 as your body adjusts. Most people experience mild or no nausea by 8 weeks. If nausea persists beyond 8 weeks or is severe, contact your GP — adjusting meal timing, eating smaller portions, or staying hydrated can help. Your prescriber may also review your dose.
Can I feel normal on Mounjaro?
Yes, most users report feeling completely normal after the initial adjustment period (usually 4–8 weeks). You should feel capable of your normal daily activities, work, and exercise. The medication works in the background — you're not meant to feel intoxicated or sedated. If you feel unwell beyond normal adjustment symptoms, contact your GP.
How does Mounjaro compare to Wegovy in terms of how you feel?
Both are GLP-1-based medications so many feelings are similar — reduced appetite, nausea, constipation. Mounjaro is a dual GIP and GLP-1 agonist whilst Wegovy (semaglutide) is GLP-1 only, so some users report slightly different intensity of appetite suppression. Individual experiences vary more than medication differences — your personal response depends on your metabolism, dose, and health.
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.