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 Quickly Does Mounjaro Suppress Appetite?
Mounjaro (tirzepatide) typically begins suppressing appetite within the first few days to two weeks of starting treatment, though the timing and intensity vary between individuals. Most people notice noticeable appetite reduction within 4 to 8 weeks as their dose is gradually increased. This appetite suppression is one of the key mechanisms that helps support weight management, working alongside a reduced-calorie diet and increased physical activity. Your GP or prescriber will monitor your response and adjust your dose accordingly during the titration phase.
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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.
When Does Appetite Suppression Begin?
Appetite suppression from Mounjaro (tirzepatide) typically begins within 3 to 7 days of your first injection for many people, though some individuals notice effects within 24 to 48 hours. However, the degree of appetite reduction is usually mild at the starting dose of 2.5 mg. As your dose is gradually increased every 4 weeks through the dose titration schedule, appetite suppression becomes more pronounced. Most people report noticeable appetite reduction by 4 to 8 weeks into treatment as they reach higher doses (5 mg to 7.5 mg and beyond). Your individual response depends on factors including body weight, metabolism, prior GLP-1 exposure, and how your body's GLP-1 and GIP receptors respond. This is why a prescriber tracks your progress and adjusts timing based on your personal experience rather than applying a one-size-fits-all timeline.
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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.
What to Expect at Each Dose Level
At 2.5 mg (weeks 1–4), appetite reduction is typically subtle or minimal. At 5 mg (weeks 5–8), most people report mild to moderate appetite reduction. At 7.5 mg to 10 mg (weeks 9–16), appetite suppression becomes more noticeable, with many people eating significantly smaller portions and feeling satisfied sooner. At 12.5 mg to 15 mg (weeks 17+), appetite suppression is typically strong, though some people experience plateauing effects over time. Early side effects like nausea can temporarily affect appetite independently of the medication's intended appetite-suppressing mechanism. Try our free GLP-1 weight loss calculator above to estimate potential outcomes at different dose levels alongside lifestyle 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.
Will Mounjaro suppress my appetite immediately on the first dose?
Most people notice some appetite reduction within days, but it is usually mild at the 2.5 mg starting dose. Significant appetite suppression typically develops over 4 to 8 weeks as your dose increases. Individual responses vary — some feel effects sooner, others take longer.
Does nausea from Mounjaro affect appetite suppression?
Yes. Early nausea (a common side effect) can reduce appetite independently of Mounjaro's intended mechanism. This nausea often improves within 2 to 3 weeks as your body adjusts, while true appetite suppression from the medication continues to build.
Can appetite suppression from Mounjaro wear off over time?
Some people report that appetite suppression plateaus or reduces slightly after several months on the same dose. This is one reason why prescribers may continue dose escalation. However, appetite typically remains lower than baseline. Individual experience varies significantly.
How does Mounjaro's tirzepatide differ from other weight loss injections like Wegovy in terms of appetite suppression?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1-only agonist. The dual mechanism of Mounjaro may produce stronger appetite suppression in clinical trials, though results vary. Your prescriber can advise which is suitable for you.
What should I do if Mounjaro isn't suppressing my appetite enough?
This requires discussion with your GP or prescriber. They may continue dose escalation if you haven't reached 15 mg, review whether you've allowed 4 weeks at each dose, or assess whether the medication is appropriate for you. Don't adjust doses yourself — always follow your prescriber's guidance.
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.