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 Long Do The Effects Of Mounjaro Last?
The effects of Mounjaro (tirzepatide) typically begin to wear off within days to weeks after you stop taking the injection, though the exact timeline varies between individuals. Clinical data shows that appetite suppression and weight management benefits are usually felt within the first few weeks of starting treatment, but they don't persist indefinitely once you stop your prescription. Understanding how long the medication works and what happens after is important for planning your long-term weight management approach with your GP.
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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 Quickly Does Mounjaro Wear Off?
Mounjaro leaves your system relatively quickly compared to some other medications. Most people notice the appetite-suppressing effects start to reduce within 3 to 7 days after their last injection, as the tirzepatide concentration in your blood gradually decreases. However, some effects may linger for up to two weeks in certain cases, depending on your metabolism and individual body composition.
- By week 1 after stopping: appetite and hunger signals typically begin returning to normal levels
- By week 2–3: most people notice their eating patterns shifting back toward pre-Mounjaro habits
- Nausea and other gastrointestinal side effects usually resolve within days of stopping
The KwikPen device delivers a pre-set dose each week, so there's no gradual tapering — when you stop, the medication effects naturally decline as your body metabolises the tirzepatide. This is different from some other medications that require a phased withdrawal.
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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 To Weight After Stopping Mounjaro?
Weight regain after stopping Mounjaro is common and expected. Clinical data suggests that without continued medication and ongoing lifestyle changes, most people gradually regain weight over several months. The rate of regain varies significantly — some regain 30–50% of lost weight within 6 months, while others maintain more of their loss depending on whether they've maintained the dietary and activity changes made during treatment.
This is why Mounjaro works best as part of a long-term approach: medication supports behaviour change, but the eating habits and physical activity improvements you build during treatment need to continue. Your GP or prescriber can discuss whether Mounjaro is intended as a short-term intervention or longer-term maintenance therapy for your individual situation. Using our GLP-1 weight loss calculator can help you understand projected timelines for both weight loss and maintenance planning.
- 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.
Can I take Mounjaro on and off, or do I need to use it continuously?
Mounjaro is typically prescribed as an ongoing treatment rather than an on-and-off medication. If you stop taking it, the effects wear off within days to weeks and weight regain usually follows. Your prescriber will discuss with you whether long-term use, temporary use, or breaks in treatment are appropriate for your individual health situation.
How long does it take for Mounjaro to leave your system completely?
Tirzepatide is largely metabolised within 7–14 days after your last injection, though trace amounts may remain longer. The appetite-suppressing effects typically wear off within the first week, which is when most people notice their hunger returning to baseline levels.
What should I do if I want to stop Mounjaro?
Always discuss stopping Mounjaro with your GP or prescriber first — don't stop suddenly without guidance. They can advise you on the best approach, whether that's gradual adjustment of your lifestyle habits before stopping, or a plan to help prevent rapid weight regain. If you're on a Mounjaro UK prescription, your prescriber will provide clear stopping guidance.
Does weight come back immediately after stopping Mounjaro?
Weight regain is gradual rather than immediate, typically occurring over weeks to months after stopping. The pace depends on whether you maintain the dietary and physical activity changes you made during treatment. Clinical data shows variability, but many people begin noticing increased appetite and modest weight increases within the first 2–4 weeks.
Is Mounjaro the same as Wegovy, and do they wear off the same way?
No. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Both wear off within days to weeks, but Mounjaro and Wegovy have different mechanisms and dose ranges. Your prescriber can compare how they may work differently for your situation.
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.