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 Co Codamol Together?
If you're taking Mounjaro (tirzepatide) for weight management and need pain relief, you may wonder whether co-codamol is safe to use alongside it. The short answer is that co-codamol can generally be taken with Mounjaro, but there are important considerations you should discuss with your GP or prescriber first. Both medications work in different ways, but certain side effects and digestive interactions require careful attention.
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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 Co Codamol Work Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — a weekly injection that helps regulate appetite and blood sugar. It works by activating natural hormone pathways to support weight management, typically alongside a reduced-calorie diet and increased physical activity.
Co-codamol is a combination painkiller containing paracetamol and codeine — an opioid pain reliever. It's used for moderate pain, such as headaches, dental pain, or period pain. Unlike Mounjaro, co-codamol works directly on pain signals in the nervous system.
Because these medications work through completely different mechanisms, there is no direct pharmacological interaction between them. However, Mounjaro's known side effects — particularly nausea, constipation, and diarrhoea — can overlap with or be affected by co-codamol use.
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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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Important Considerations Before Taking Both Medicines
Codeine and constipation: Codeine (in co-codamol) is known to cause constipation. Since many people on Mounjaro already experience constipation as a side effect, combining these medications could make this worse. Conversely, some people on Mounjaro experience diarrhoea — in which case co-codamol may help balance this.
Nausea and stomach upset: Both medications can affect your digestive system. Mounjaro commonly causes nausea, especially at higher doses or when first starting. Co-codamol may add to this effect or, rarely, cause additional gastrointestinal issues.
Always inform your prescriber: Before taking co-codamol while on Mounjaro, tell your GP or the prescriber who issued your Mounjaro prescription. They can assess your individual circumstances and advise whether it's appropriate, or suggest an alternative painkiller if needed.
- 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 co-codamol while on Mounjaro?
Co-codamol and Mounjaro do not have a direct pharmacological interaction. However, you should inform your GP or prescriber before taking them together, as codeine can worsen constipation and both medications may affect your digestion differently. Your prescriber can assess your specific health situation and advise whether it's appropriate.
Will co-codamol affect how Mounjaro works?
Co-codamol is unlikely to reduce the effectiveness of Mounjaro, as they work through completely different mechanisms. However, like all oral medications taken alongside Mounjaro, there may be a minor effect on absorption due to slowed gastric emptying. Discuss timing of doses with your GP.
What painkiller alternatives might be safer with Mounjaro?
Paracetamol alone (without codeine) or ibuprofen are often alternatives to co-codamol and may be gentler on your digestive system while on Mounjaro. However, always check with your GP or prescriber before starting any new medication, as individual circumstances vary.
Why does Mounjaro affect digestion?
Mounjaro slows gastric emptying — how quickly food leaves your stomach — as part of its mechanism for supporting appetite regulation. This can cause nausea, constipation, or diarrhoea in the first weeks. These effects often improve over time, but they can interact with medications like co-codamol.
Should I avoid co-codamol completely while on Mounjaro?
You don't necessarily need to avoid co-codamol, but you should discuss it with your GP first. They may recommend a single-dose paracetamol instead, or advise you on the best timing or dose of co-codamol for your situation. Never stop or start any medication without professional guidance.
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