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 to Get Mounjaro Out of Your System
If you're concerned about how long Mounjaro stays in your body or want to stop taking it, you're not alone. Mounjaro (tirzepatide) is gradually eliminated from your system after you stop injecting, but the process takes time. Understanding how your body clears this medication, what to expect when stopping, and when to speak to your GP is important for managing your health safely.
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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 Is Eliminated and What Affects Clearance
Mounjaro is cleared from your body gradually over several weeks after your final injection. Tirzepatide has a half-life of approximately 5 days, meaning half of the medication is eliminated from your system every 5 days. This means after 5 days, roughly 50% remains; after 10 days, approximately 25% remains; and after about 3–4 weeks, most of the medication has been cleared from your body.
- Kidney and liver function affect how quickly Mounjaro is processed — people with reduced kidney or liver function may take longer to clear the medication
- Body weight and composition can influence clearance rates
- Age and metabolism also play a role in elimination speed
If you're stopping Mounjaro, there's no special procedure to "flush" it from your system — your body naturally eliminates it over time. However, always discuss stopping with your GP or prescriber before your final injection, especially if you have type 2 diabetes or other health conditions being managed alongside weight loss treatment.
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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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Stopping Mounjaro Safely and What to Expect
When you stop Mounjaro, side effects typically resolve as the medication clears your system — usually within 2–4 weeks. Nausea, diarrhoea, and stomach discomfort usually fade first. However, appetite typically returns gradually once the medication is no longer active, which is why weight regain is common if diet and activity levels aren't maintained.
If you've been using the Mounjaro KwikPen, simply stop administering your weekly injection. Your GP may want to monitor your weight, blood sugar (if diabetic), or other health markers after stopping. If you experienced significant side effects, discuss alternatives with your prescriber — there are other GLP-1 options available on the NHS through specialist tier 3 weight management services, such as Wegovy (semaglutide) or Saxenda (liraglutide), which may suit you better.
Rebound weight gain after stopping weight loss medication is a real concern — clinical evidence shows that without ongoing lifestyle support, most people regain weight within 6–12 months of stopping. This is why your GP or specialist will discuss a transition plan before stopping Mounjaro. Consider using our free progress tracker to monitor your weight after stopping, and use our BMI calculator to check where you sit on NHS guidelines. If you're planning to restart medication in future, your prescriber can reassess your eligibility.
- 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 long does Mounjaro stay in your system after stopping?
Mounjaro has a half-life of about 5 days, so approximately half clears every 5 days. After 3–4 weeks, most of the medication is eliminated. However, individual clearance rates vary based on kidney function, liver health, body weight, and age. Always consult your GP about your specific situation.
Can I speed up how quickly Mounjaro leaves my body?
No, there's no safe way to "flush" tirzepatide from your system faster. Your body naturally eliminates it through normal metabolic processes. Staying hydrated and maintaining regular physical activity supports overall health but won't significantly speed clearance. Never attempt extreme measures without GP guidance.
Will my appetite come back immediately after stopping Mounjaro?
No, appetite returns gradually as the medication clears over 2–4 weeks. Some people notice increased hunger within days; others take weeks. This gradual return is why weight regain risk is highest in the first 3–6 months after stopping — maintaining diet and exercise habits during this period is crucial.
Should I tell my GP before stopping Mounjaro?
Yes, absolutely. Always consult your GP or prescriber before your final injection. They need to monitor your health, especially if you have type 2 diabetes or other conditions. Your GP can discuss transition plans, alternative medications, or ongoing lifestyle support to prevent rapid weight regain.
What if I had bad side effects from Mounjaro — will they disappear once it's out of my system?
Most side effects (nausea, diarrhoea, stomach pain) resolve as Mounjaro clears, usually within 2–4 weeks. However, if you experienced serious side effects, discuss this with your GP before stopping. There may be alternative weight loss injections available through NHS tier 3 services that you tolerate better, such as Wegovy or Saxenda.
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.