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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How Long Does Mounjaro Take To Suppress Appetite?
Mounjaro can begin to reduce appetite within the first few days to weeks of starting treatment, though the effect typically becomes more noticeable after 2–4 weeks on your starting dose. The appetite-suppressing effect of tirzepatide (the active ingredient in Mounjaro) tends to build gradually as your body adjusts to the medication and as your dose increases over time. Most people report meaningful appetite reduction by week 4–8. Individual timing varies depending on your body's response, starting dose, and how quickly you progress through dose escalation.
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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's Appetite-Suppressing Mechanism Works
Mounjaro is a dual GIP and GLP-1 receptor agonist—meaning it activates two natural hormone pathways that control hunger and satiety. When you eat, your body releases GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) hormones that signal to your brain that you're full. Mounjaro amplifies these signals.
The appetite suppression works through several mechanisms:
- Central appetite reduction: Signals to the brain's hunger centres, reducing the drive to eat
- Increased satiety: Helps you feel fuller after smaller meals
- Slower gastric emptying: Food leaves your stomach more slowly, prolonging the feeling of fullness
- Reduced cravings: Many users report fewer food cravings, particularly for high-calorie foods
Unlike older weight loss medications, this dual mechanism may produce stronger appetite suppression than single GLP-1 injections like Wegovy (semaglutide). However, individual responses vary significantly based on genetics, metabolism, and lifestyle factors.
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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.
Timeline: When Appetite Suppression Typically Begins
Most people experience their first signs of appetite reduction within 3–7 days of the starting dose (2.5 mg), though this is often subtle. By week 2–3, appetite suppression becomes more noticeable for many users—meals feel more satisfying, portions naturally decrease, and snacking urges diminish. The effect typically peaks around week 4–8 on each dose.
During dose escalation (when your dose increases every 4 weeks), appetite suppression may temporarily plateau or even reduce slightly as your body adjusts to the new dose. This is normal. Full appetite-suppressing benefits at each new dose usually emerge by week 3–4 of that dose. At the maximum maintenance dose (15 mg), appetite suppression is typically at its strongest, though some users find it plateaus before reaching the highest dose.
- 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.
How quickly does appetite suppression start after my first Mounjaro injection?
Some people notice reduced hunger within 3–7 days of their first 2.5 mg injection, but for many the effect is subtle initially. More noticeable appetite suppression typically develops by week 2–4. Individual timelines vary based on body composition, metabolism, and baseline appetite levels. Your GP or prescriber can discuss what to expect based on your personal circumstances.
Will appetite suppression continue throughout my treatment with Mounjaro?
Yes, appetite suppression typically persists throughout your Mounjaro treatment. However, some users report that the effect may slightly reduce over time—a phenomenon called tachyphylaxis. If appetite suppression diminishes, dose escalation, dietary consistency, and physical activity often help maintain results. This should be discussed with your prescriber if it occurs.
Is Mounjaro's appetite suppression stronger than Wegovy?
Clinical evidence suggests Mounjaro's dual GIP and GLP-1 mechanism may produce stronger appetite suppression and greater weight loss than single GLP-1 medications like Wegovy. In the SURMOUNT trial, Mounjaro showed average weight loss of 15–21% at various doses, compared to approximately 15% for Wegovy in the STEP trial. However, individual responses vary—some people respond better to one medication than the other.
What should I do if I'm not feeling appetite suppression after 4 weeks?
If appetite suppression hasn't developed noticeably by week 4–6, discuss this with your prescriber. It may be normal variation in response, or it could indicate that your dose needs adjusting. Ensure you're also following a structured eating plan and staying hydrated—Mounjaro works best alongside lifestyle changes, not instead of them. Your prescriber may recommend dose escalation or review your overall approach.
Can I use the MyWeightCheck GLP-1 weight loss calculator to estimate results?
Yes, our free GLP-1 weight loss calculator can help you project potential weight loss at different Mounjaro doses based on clinical trial data. This gives you a realistic expectation of outcomes and can help you track progress over time. Remember that individual results vary—appetite suppression and weight loss depend on your adherence, diet, and physical activity, not just the medication dose.
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.