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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Mounjaro and Quetiapine: What You Need to Know
If you're taking quetiapine and considering Mounjaro (tirzepatide), it's important to understand how these medications interact. Quetiapine is an antipsychotic medication used to treat schizophrenia, bipolar disorder, and depression, while Mounjaro is a GLP-1 receptor agonist prescribed for weight management in eligible UK adults. Both medications can affect your digestive system and metabolism, so discussing the combination with your GP or prescriber is essential before starting any new treatment.
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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 May Interact with Quetiapine
Mounjaro (tirzepatide) slows how quickly food moves through your stomach — a process called gastric emptying. This effect can reduce nausea and appetite. Quetiapine, meanwhile, can affect metabolism and may increase hunger or cravings in some people. When used together, these opposing effects need careful monitoring.
- Mounjaro may slow the absorption of oral medications, including some antipsychotics like quetiapine
- This could potentially reduce how effectively quetiapine works in your body
- Changes in appetite and blood sugar control can also be affected by the combination
- Your prescriber may need to adjust quetiapine dosing or monitor you more closely
There is no absolute contraindication between Mounjaro and quetiapine — they can be used together, but only under close medical supervision and with full disclosure to your prescriber about both medications.
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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 You Must Do Before Starting Mounjaro
Before beginning Mounjaro treatment, inform your prescriber that you take quetiapine. This is essential information for your clinical assessment. Your prescriber will review your current medications, mental health stability, and weight management goals to decide whether Mounjaro is appropriate for you.
If approved, your prescriber may recommend more frequent check-ups to monitor how both medications work together. You should also report any changes in your mental health symptoms, mood, appetite, or weight to your GP. Never adjust or stop quetiapine without guidance from your psychiatrist or GP — even if starting Mounjaro.
- 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 and quetiapine at the same time?
Yes, they can be used together, but only under medical supervision. Mounjaro may slow the absorption of quetiapine, so your prescriber may need to monitor you more closely or adjust quetiapine dosing. Always inform your prescriber about both medications before starting Mounjaro treatment.
Will Mounjaro affect how my quetiapine works?
Mounjaro can slow gastric emptying, which may reduce how quickly quetiapine is absorbed into your bloodstream. This doesn't necessarily mean quetiapine will stop working, but your prescriber may need to adjust your dose or monitor your mental health symptoms more carefully during the first few weeks.
What should I tell my prescriber about using both medications?
Inform your prescriber that you take quetiapine, the dose you take, and why you take it (schizophrenia, bipolar disorder, depression, etc.). Also mention any side effects you currently experience from quetiapine, your current weight, BMI, and any weight-related health conditions. This helps them assess whether Mounjaro is safe and appropriate for you.
What side effects might happen if I take both medications together?
Combined side effects could include nausea, diarrhoea, constipation, dizziness, fatigue, and changes in appetite or blood sugar. Mounjaro commonly causes gastrointestinal side effects, so these may be more noticeable when combined with quetiapine. Report any concerning symptoms to your GP immediately.
Can I adjust my quetiapine dose when starting Mounjaro?
No — never adjust or stop quetiapine without guidance from your psychiatrist or GP. Stopping antipsychotic medication abruptly can be dangerous. If you and your prescriber decide Mounjaro is suitable, they will manage any necessary adjustments to quetiapine dosing as part of your overall treatment plan.
Ready to take control of your weight loss journey?
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