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 Do The Effects Of Mounjaro Last?
Mounjaro (tirzepatide) is a prescription-only GLP-1 and GIP receptor agonist that helps reduce appetite and support weight loss. Many people wonder how long the medication's effects last once they start treatment—and crucially, what happens if they stop. The duration and sustainability of Mounjaro's effects depend on several factors, including dose, how long you've been taking it, and your individual response. Understanding this timeline helps you make an informed decision about whether this medication is right for your weight management journey.
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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 Effects Work And Last Over Time
Mounjaro begins working relatively quickly, with most people noticing reduced appetite within the first few weeks of starting or increasing their dose. The medication reaches steady state after about 4–5 weeks on the same dose, meaning your body has accumulated enough to deliver consistent appetite-suppressing effects. As your dose increases through the titration schedule—from 2.5 mg up to the maximum 15 mg—the effects typically become more pronounced, with most people reaching their target dose around week 17 onwards.
- Week 1–4: Initial adjustment period; appetite reduction may be mild
- Week 5–8: Effects become more noticeable as the dose accumulates
- Week 9–16: Progressive dose increases (7.5 mg, 10 mg, 12.5 mg) gradually intensify appetite suppression
- Week 17+: Maintenance dose (typically 15 mg) provides consistent effects
Clinical trials showed that weight loss continues throughout the treatment period, with the greatest losses often seen after 12–20 weeks of treatment. However, individual responses vary significantly—some people see rapid appetite reduction, whilst others experience a more gradual effect.
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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 Happens When You Stop Taking Mounjaro
If you stop taking Mounjaro, the appetite-suppressing effects typically begin to fade within 2–4 weeks. This is because tirzepatide is cleared from your body relatively quickly once injections stop. Most people find their appetite returns towards baseline levels within 4–8 weeks, though the exact timeline varies depending on your individual metabolism and how long you've been taking the medication.
This is why NHS specialist services and private prescribers emphasise that Mounjaro works best alongside sustained lifestyle changes—diet and physical activity habits formed during treatment are more likely to persist even if you eventually stop the medication. Many people continue on Mounjaro longer-term because stopping may result in weight regain if dietary and exercise habits return to pre-treatment patterns. Your prescriber can discuss whether ongoing treatment, dose maintenance, or a planned stop is right for you.
- 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 Mounjaro start working?
Most people notice reduced appetite within the first 1–2 weeks of starting or increasing their dose, though effects become more consistent after 4–5 weeks as the medication builds up in your system. The full appetite-suppressing effect may not be apparent until you've been on a stable dose for several weeks.
Does Mounjaro's effectiveness wear off over time?
No—clinical trial data shows that Mounjaro's weight loss effects remain consistent when you continue taking it at the same dose. You don't develop tolerance. However, your prescriber may adjust your dose based on your response and individual health needs.
Can I use our GLP-1 weight loss calculator to estimate how long results will take?
Yes. Our free weight loss calculator on this page can help you project potential weight loss timelines at different Mounjaro doses, based on clinical trial data. This gives you a realistic sense of expected results over weeks and months, though individual outcomes vary significantly.
What happens to my weight if I stop Mounjaro?
If you stop Mounjaro, appetite suppression typically fades within 2–4 weeks, and hunger returns towards baseline within 4–8 weeks. Weight regain is possible if you don't maintain the diet and exercise habits formed during treatment. This is why long-term lifestyle changes are essential alongside medication.
Does a higher Mounjaro dose last longer than a lower dose?
No—both lower and higher doses last a similar length of time once you stop. A 15 mg dose and a 5 mg dose both take 2–4 weeks to begin losing effect after your final injection. The difference is that higher doses typically produce greater appetite suppression and weight loss during active treatment.
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.