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 Quickly Does Mounjaro Suppress Appetite?
Mounjaro (tirzepatide) and Wegovy (semaglutide) both work to reduce appetite, but the onset and intensity differ. Most users report noticeable appetite suppression within the first 1–2 weeks on the starting dose, though the full effect builds over several weeks as doses increase. The difference? Mounjaro uses a dual GIP and GLP-1 mechanism, whilst Wegovy activates GLP-1 only. This section explains the timeline, compares clinical evidence, and helps you understand what happens when you start either medication in the UK.
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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.
Timeline and Mechanism — Mounjaro vs Wegovy
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist. The GIP mechanism may contribute to faster appetite suppression in some users, though evidence is still emerging. Most people report reduced appetite within 3–7 days of the starting dose (2.5 mg), with effects intensifying over 2–4 weeks.
Wegovy (semaglutide), a GLP-1 only agonist, typically shows appetite suppression within 1–2 weeks of the starting dose (0.25 mg). The effect builds gradually as doses escalate every 4 weeks.
- Mounjaro: Appetite reduction often noticeable by day 7–10
- Wegovy: Appetite reduction typically by week 2
- Both: Full benefit requires 16+ weeks to reach maintenance dose
- Individual variation is significant — some feel effects immediately, others take 3–4 weeks
Clinical trial data shows both medications significantly reduce appetite, but timing varies between individuals. Using our GLP-1 weight loss calculator can help you project potential outcomes at different doses.
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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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Practical Differences — What This Means for You
If faster appetite suppression is important to you, clinical evidence slightly favours Mounjaro's dual mechanism, though individual responses vary widely. However, eligibility, NHS or private access, and side effect tolerance may be more decisive factors than timing alone.
Both medications require a prescription and clinical assessment through either an NHS specialist weight management service or a UK-licensed private prescriber. Your prescriber will consider your medical history, current medications, and lifestyle to determine which is more suitable. You can calculate your BMI using our free BMI calculator to understand your eligibility baseline, but a healthcare professional must assess you individually.
Appetite suppression is one benefit — both also slow gastric emptying and improve satiety, meaning you feel fuller longer. Most users report the most dramatic appetite reduction occurs in weeks 4–8 as doses increase, not immediately at the starting 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.
Does Mounjaro suppress appetite faster than Wegovy?
Clinical evidence suggests Mounjaro may suppress appetite slightly faster (within 3–7 days for some users) compared to Wegovy (1–2 weeks), owing to its dual GIP and GLP-1 mechanism. However, individual variation is significant, and many users report similar timelines. Your prescriber can advise which is most suitable for your circumstances.
How long before Mounjaro's appetite-suppressing effects start?
Most people notice reduced appetite within the first 1–2 weeks on the 2.5 mg starting dose. Effects intensify as doses increase every 4 weeks. Full appetite suppression typically occurs around weeks 4–8 when reaching a therapeutic dose. Some users feel effects by day 3–5; others take longer.
What's the difference between Mounjaro's and Wegovy's mechanisms?
Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy is GLP-1 only. The dual mechanism in Mounjaro may offer additional satiety benefits, though both reduce hunger and slow gastric emptying. Clinical trials show both are effective for appetite suppression and weight loss.
Can I get Mounjaro or Wegovy through the NHS in the UK?
Both are available through NHS specialist tier 3 weight management services, though access varies by region and waiting lists can be lengthy. Both are also available privately through UK-licensed online prescribers following a clinical assessment. Your GP can refer you to NHS services or you can seek private assessment.
Will appetite suppression with Mounjaro be permanent when I stop?
No. Appetite suppression is an active effect of the medication. When you stop injections, appetite typically returns to baseline within 1–2 weeks. This is why long-term lifestyle changes (diet and exercise) are essential for maintaining weight loss after stopping treatment.
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