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 Duloxetine With Mounjaro?
If you're taking duloxetine (an antidepressant) and considering Mounjaro (tirzepatide) for weight management, it's important to understand how these medications interact. Duloxetine and Mounjaro can be used together, but your prescriber needs to know about all medications you're currently taking before starting any weight loss treatment. This guide explains the key considerations and what to discuss with your GP or prescriber 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.
Key Medication Interactions and NHS Prescribing
Duloxetine is an SNRI (serotonin-noradrenaline reuptake inhibitor) used to treat depression, anxiety, and chronic pain. Mounjaro (tirzepatide) is a GIP and GLP-1 receptor agonist — a dual-action weight management injection licensed in the UK. There is no direct pharmacological interaction between these two medications, meaning they do not significantly interfere with each other's mechanism of action.
- Duloxetine works on neurotransmitters in the brain; Mounjaro works on appetite hormones and blood sugar regulation
- Both can cause nausea — managing this side effect together requires careful monitoring
- Your prescriber will assess whether both medications are appropriate for you based on your overall health
- Any changes to Mounjaro dosing (dose titration) should be discussed with your GP to ensure mental health support continues
Always inform your prescriber about duloxetine before starting Mounjaro. If you're prescribed tirzepatide through NHS specialist services or privately, your clinical assessment will include a full medication history.
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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 to Discuss With Your GP or Prescriber
Before starting Mounjaro, tell your prescriber that you take duloxetine. They will consider:
- How duloxetine affects your appetite and nausea baseline
- Whether any dose adjustments to either medication are needed
- Your mental health support during weight management treatment
- How to manage nausea if it occurs with Mounjaro — this is a common side effect
- Your full medical history, BMI, and eligibility under NHS NICE guidance or private prescribing criteria
If you experience new or worsening symptoms after starting Mounjaro, contact your GP promptly. Weight loss and medication changes can interact with mental health management, so maintaining open communication with your healthcare team is essential.
- 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 duloxetine and Mounjaro together?
Yes, duloxetine and Mounjaro can generally be used together. There is no direct pharmacological interaction between an SNRI antidepressant and tirzepatide. However, your prescriber must know you take duloxetine before starting Mounjaro. Both medications can cause nausea, so your prescriber will monitor you carefully and adjust if needed.
Will Mounjaro interfere with my duloxetine effectiveness?
Mounjaro works on appetite hormones and blood sugar, not on the same neurotransmitter pathways as duloxetine. It should not reduce duloxetine's antidepressant effect. However, weight loss and lifestyle changes during Mounjaro treatment can positively support mental health. Always discuss any mood changes with your GP.
What side effects might I experience taking both medications?
The main shared side effect is nausea — very common with Mounjaro. Duloxetine can also cause nausea in some people. Your prescriber will start Mounjaro at a low dose (2.5 mg) and increase gradually, allowing your body to adjust. Report any persistent nausea or mental health changes to your GP immediately.
Do I need to change my duloxetine dose if I start Mounjaro?
Not necessarily. Mounjaro does not directly affect duloxetine levels. However, if you experience significant nausea or other changes, your prescriber may review both medications. Never change duloxetine without discussing it with your GP — stopping antidepressants suddenly can be harmful.
How do I access Mounjaro in the UK if I take duloxetine?
You can access Mounjaro through NHS specialist tier 3 weight management services (via GP referral) or private prescribing. Either route requires a clinical assessment. Inform your prescriber or NHS clinician about duloxetine, your BMI, and any weight-related health conditions. Use our free BMI calculator above to check your eligibility baseline, then discuss options with your GP.
Ready to take control of your weight loss journey?
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