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 and Duloxetine Together?
Mounjaro (tirzepatide) and duloxetine are medications that work in different ways, but they may be prescribed together if clinically appropriate. Mounjaro is a weight management injection, whilst duloxetine is an antidepressant used to treat depression and anxiety. Before taking both medications, it's important to understand potential interactions and what your GP or prescriber needs to know. This guide explains the safety considerations for using these medications together in the UK.
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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.
What You Need to Tell Your Prescriber
When seeking a prescription for Mounjaro, always inform your healthcare provider that you are taking duloxetine. Your prescriber needs this information to assess whether Mounjaro is safe for you and whether any dose adjustments are needed. Mounjaro may affect how quickly your stomach empties and how your body absorbs other medications, so your prescriber must know about all medications you are currently taking. If you're prescribed Mounjaro through an NHS specialist weight management service or a private online prescriber, ensure you disclose duloxetine on your medical questionnaire or during your consultation. Do not start or stop duloxetine without discussing it with your GP first, and do not make changes to either medication without medical guidance.
- Inform your prescriber of all medications, including duloxetine
- Disclose any mental health conditions or treatments
- Report any new or worsening mood changes after starting Mounjaro
- Keep your GP updated on both medications regularly
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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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Mounjaro Dose Titration and Medication Interactions
Mounjaro is prescribed at gradually increasing doses, starting at 2.5 mg and increasing to a maximum of 15 mg over several weeks. Because Mounjaro slows gastric emptying in the early weeks, it may temporarily affect how duloxetine is absorbed. However, this effect typically reduces as your body adjusts to Mounjaro over time. There are no specific known dangerous interactions between tirzepatide and duloxetine reported in clinical trials, but individual responses vary. Your prescriber will monitor you for any adverse effects and adjust your treatment plan if needed. If you experience new side effects or changes in how your duloxetine is working after starting Mounjaro, report this to your GP or prescriber immediately. Use our free BMI calculator to assess your weight management needs, and our GLP-1 weight loss calculator to understand potential outcomes with Mounjaro if it's prescribed to 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.
Can I take Mounjaro and duloxetine at the same time?
There are no absolute contraindications between Mounjaro and duloxetine reported in clinical data, meaning they can potentially be taken together. However, your prescriber must assess your individual health to confirm this is safe for you. Always disclose duloxetine when applying for Mounjaro.
Will Mounjaro affect how duloxetine works?
Mounjaro slows gastric emptying, which may temporarily affect absorption of oral medications like duloxetine. This effect typically decreases over time as your body adjusts. If you notice changes in your mood or mental health symptoms after starting Mounjaro, tell your GP immediately.
What if I'm on duloxetine and want to start Mounjaro?
Speak to your GP or the prescriber conducting your Mounjaro assessment. Provide full details of your duloxetine dose and how long you've been taking it. Your prescriber will decide if Mounjaro is appropriate and monitor you for any interactions.
Should I stop duloxetine before starting Mounjaro?
No — do not stop or change duloxetine without medical guidance. Stopping antidepressants abruptly can cause withdrawal symptoms. Your prescriber will advise whether any adjustments are needed and how to manage both medications safely together.
What are the signs of an adverse interaction to watch for?
Monitor for unusual changes in mood, increased anxiety, nausea beyond typical Mounjaro side effects, dizziness, or serotonin syndrome symptoms (rapid heartbeat, muscle stiffness, high fever). Contact your GP immediately if you experience these while taking both medications.
Ready to take control of your weight loss journey?
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