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 sometimes used together, but it's important to understand how they interact. Mounjaro is a prescription weight management injection, while duloxetine is an antidepressant and anxiety medication. This guide explains what you need to know about combining these medications safely in the UK, and why speaking with your GP or prescriber is essential before starting either medication if you're already taking the other.
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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 These Medications Work
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — a once-weekly injection that may help reduce appetite and support weight management alongside diet and physical activity. It works by activating two natural hormone pathways in the body.
Duloxetine is a serotonin-noradrenaline reuptake inhibitor (SNRI) antidepressant. It's prescribed for depression, anxiety, fibromyalgia, and chronic pain conditions. Duloxetine works by increasing levels of certain neurotransmitters in the brain.
Neither medication directly interacts with the other at a chemical level, but there are practical considerations you should know about when taking both together.
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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 Need to Tell Your Prescriber
Before starting Mounjaro, always inform your GP or prescriber that you're taking duloxetine. Similarly, if you're starting duloxetine while already taking Mounjaro, inform your prescriber. This is important because:
- Duloxetine can affect appetite and gastric function, which may combine with Mounjaro's effects on stomach emptying
- Some antidepressants can affect how your body processes medications
- Your prescriber may need to monitor you more carefully or adjust doses
- Both medications can cause nausea — combining them may increase this effect
Never start or stop either medication without consulting your healthcare team. Your GP can assess whether this combination is safe for your individual health situation.
- 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 and duloxetine at the same time?
There is no direct chemical interaction between Mounjaro and duloxetine, so they can potentially be used together. However, both medications can affect appetite and stomach function, and both may cause nausea. Always inform your prescriber about all medications you're taking — they will assess whether this combination is appropriate for you.
Can Mounjaro and duloxetine affect each other's effectiveness?
Mounjaro works on appetite hormones, while duloxetine works on neurotransmitters in the brain — different mechanisms. However, duloxetine's effects on appetite may interact with Mounjaro's appetite-suppressing effects. Your prescriber will consider this when assessing your suitability for treatment.
What side effects might I experience if I take both medications?
Both Mounjaro and duloxetine can cause nausea, dizziness, and gastrointestinal symptoms. Taking them together may increase the risk of these effects. Monitor how you feel and report any concerning symptoms to your GP. Your prescriber may adjust doses or timing to minimise side effects.
Will duloxetine affect how my body absorbs Mounjaro?
Mounjaro is injected, so it bypasses the digestive system — duloxetine is unlikely to affect Mounjaro's absorption. However, Mounjaro slows gastric emptying, which may affect how quickly oral medications like duloxetine are absorbed. Your prescriber will advise on optimal medication timing.
What should I do if I'm currently taking duloxetine and want to try Mounjaro?
Speak to your GP first. They can review your current medications, assess your weight management needs, check your eligibility for Mounjaro based on BMI and health conditions, and confirm that this combination is safe for you. Never start Mounjaro without consulting your healthcare team, even if you've seen it available privately online.
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