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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When Does Appetite Suppression Start With Mounjaro?
Appetite suppression with Mounjaro typically begins within the first 1–2 weeks of starting treatment, though the effect builds gradually as your dose increases over the initial 4–5 months. Unlike some medications, Mounjaro (tirzepatide) works through a dual GIP and GLP-1 receptor mechanism, which may explain why many users report noticeable appetite changes relatively quickly. However, timing varies significantly between individuals — some feel effects within days, while others take several weeks. This guide compares Mounjaro's appetite suppression timeline with Wegovy and explains what clinical evidence tells us about both medications.
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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 Appetite Suppression Works: Mounjaro vs Wegovy
Mounjaro (tirzepatide) activates two hormone pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual mechanism may produce appetite suppression more rapidly than single-action medications. The tirzepatide SURMOUNT clinical trials showed that participants began experiencing reduced hunger and food cravings within the first weeks of treatment, with effects intensifying as doses increased from 2.5mg to 15mg over approximately 20 weeks.
Wegovy (semaglutide) activates only the GLP-1 pathway. The STEP clinical trials demonstrated appetite reduction, but the single mechanism typically produces a slower onset — many users report noticeable appetite changes by weeks 3–4 rather than weeks 1–2. Wegovy's dose titration is also longer, starting at 0.25mg and escalating to 2.4mg over approximately 16 weeks.
- Mounjaro: dual mechanism, potentially faster onset
- Wegovy: single mechanism, gradual onset
- Individual variation is significant — prescriber guidance essential
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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.
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Timeline Expectations and Individual Factors
Most users report noticing appetite suppression with Mounjaro between week 1 and week 4 of starting treatment, though some experience changes within 3–5 days. The effect typically deepens as your dose increases — moving from 2.5mg to 5mg to 10mg produces cumulative appetite changes. Factors affecting onset include your individual metabolism, existing hunger patterns, food triggers, and how your body responds to the GIP/GLP-1 pathways.
It's important to remember that appetite suppression alone is not the same as weight loss. Your GP or prescriber will assess whether Mounjaro is suitable for you based on your individual health profile. Use our free BMI calculator and GLP-1 weight loss calculator above to understand your baseline and projected changes — this gives you realistic expectations alongside medical supervision.
- 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.
Does Mounjaro work faster than Wegovy for appetite suppression?
Clinical evidence suggests Mounjaro's dual GIP+GLP-1 mechanism may produce faster initial appetite suppression than Wegovy's single GLP-1 mechanism. However, individual responses vary significantly. Some users notice effects within days, others within weeks. Your prescriber will assess which medication suits your personal health profile — this is not a choice based on speed alone.
What happens if I don't feel appetite suppression in the first week?
Delayed appetite suppression is normal and does not mean Mounjaro isn't working. Some people experience other effects first (nausea, for example) before appetite changes become apparent. Continue your treatment plan as prescribed — effects typically accumulate over the first 4–8 weeks as your body adjusts and doses increase. Contact your prescriber if you have concerns.
Can I expect appetite suppression to continue indefinitely?
Appetite suppression effects often stabilise after the first 8–12 weeks of treatment as your body adapts. Some users maintain strong appetite reduction, others experience a modest return of hunger — this is normal. Your prescriber may adjust your dose or discuss lifestyle strategies. Remember that these medications work best alongside a reduced-calorie diet and increased physical activity, not instead of them.
How is appetite suppression measured in clinical trials?
In the SURMOUNT and STEP trials, appetite suppression was measured using validated scales like the Three-Factor Eating Questionnaire (TFEQ), alongside actual weight loss outcomes. Both trials showed significant reductions in hunger and increased feelings of fullness. SURMOUNT (Mounjaro) showed slightly larger appetite-related improvements, but both medications demonstrated substantial effects compared to placebo.
Will my GP prescribe Mounjaro based on appetite suppression alone?
No. Prescription weight loss medications like Mounjaro are prescribed based on your BMI, weight-related health conditions, and overall health profile — not appetite sensations. Your GP or specialist will assess your eligibility using NHS guidelines. Appetite suppression is one mechanism that supports weight loss, but it's not the only factor considered in treatment decisions.
Ready to take control of your weight loss journey?
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