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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Can You Take Mounjaro With Quetiapine?
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 conditions like schizophrenia and bipolar disorder, whilst Mounjaro is a prescription weight management injection. There is no direct pharmacological interaction between tirzepatide and quetiapine, but your prescriber must assess your individual situation before starting any new medication. Always inform your GP or prescriber of all current medications, including quetiapine, before beginning Mounjaro.
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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 And Quetiapine Work In Your Body
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist that works by activating two natural hormone pathways to help regulate appetite and support weight management. It slows how quickly food leaves the stomach and may reduce food cravings alongside a reduced-calorie diet and increased physical activity.
Quetiapine is an antipsychotic that works on dopamine and serotonin receptors in the brain to manage psychiatric symptoms. Unlike Mounjaro, it works through a completely different mechanism and does not directly interact with GIP or GLP-1 pathways.
Because these medications work through entirely separate pathways, there is no known direct pharmacological interaction between tirzepatide and quetiapine. However, this does not mean you can start Mounjaro without medical assessment — your prescriber must review your complete medical history and all current medications to ensure safety.
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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.
Important Considerations Before Starting Mounjaro
If you're taking quetiapine, your prescriber needs to know this before assessing you for Mounjaro. Whilst there is no direct drug interaction, several important factors must be considered:
- Quetiapine can affect weight and appetite, so your prescriber will want to understand your baseline weight and any changes you've experienced
- Mounjaro can cause nausea, diarrhoea, and reduced appetite, which may be more noticeable if you're already experiencing appetite changes from quetiapine
- Both medications can affect blood sugar control — your GP may want to monitor this more closely
- Mounjaro slows gastric emptying, which could theoretically affect the timing of quetiapine absorption, though this is not a significant clinical concern
Your prescriber will weigh these factors and decide whether Mounjaro is appropriate for you. Use our free GLP-1 weight loss calculator to explore potential weight loss outcomes if your prescriber gives the go-ahead.
- 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.
Is it safe to take Mounjaro if I'm already on quetiapine?
There is no direct pharmacological interaction between tirzepatide and quetiapine. However, safety depends on your individual health profile. You must inform your prescriber of all medications, including quetiapine, before starting Mounjaro. They will assess whether it's appropriate for you based on your complete medical history.
Will quetiapine affect how Mounjaro works?
Quetiapine does not directly affect Mounjaro's mechanism of action, as they work through different pathways. However, both medications can affect appetite and weight, so your prescriber may monitor your response more carefully to ensure you're tolerating both medications well.
Can Mounjaro be prescribed alongside quetiapine on the NHS?
NHS access to Mounjaro is through specialist tier 3 weight management services. If you're taking quetiapine, your weight management specialist will review this and decide whether Mounjaro is suitable. Some regional NHS services may be cautious and request additional monitoring.
What should I tell my prescriber about quetiapine before starting Mounjaro?
Tell your prescriber the exact dose of quetiapine, how long you've been taking it, any side effects you experience (especially appetite or weight changes), and any other psychiatric or physical health conditions. This helps them assess whether Mounjaro is safe and appropriate for you.
Are there any side effects more likely when combining Mounjaro and quetiapine?
Both can cause nausea and affect appetite. Mounjaro may cause GI side effects like diarrhoea or constipation. If you experience severe or persistent side effects when taking both, contact your GP or prescriber immediately — they may need to adjust either medication.
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.