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Can I take Codeine and Magnesium together?

Drug interaction guide

Taking magnesium and codeine together can lead to increased drowsiness and may cause constipation. Magnesium can also slightly interfere with how your body absorbs codeine if taken at the exact same time.

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Why this happens

Both substances can slow down the central nervous system, leading to an additive calming or sedating effect. Additionally, magnesium (especially in antacid form) can change the acidity of the stomach, which may slightly alter how quickly codeine enters your system. Both can also slow down the movement of the digestive tract.

It is generally safe to take these together, but you should be aware that you might feel more tired or sleepy than usual. To ensure the codeine works effectively, try to leave a gap of 2 hours between taking a magnesium supplement (or antacid) and your codeine dose. If you experience severe constipation, speak to a pharmacist.

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Taking multiple medicines? Our Medicines Interaction Checker helps you check whether your prescriptions, over-the-counter medicines, and supplements are safe to take together. Simply search for your medicines to see potential interactions and what to do about them.

Disclaimer

This information is for general educational purposes only and should not be relied upon as a substitute for professional medical advice. Always consult your GP, pharmacist, or another qualified healthcare professional before making decisions about your medications. Individual circumstances may vary, and only a healthcare professional who knows your medical history can provide personalised guidance.

Article history

The information on this page is written and peer reviewed by qualified clinicians.

  • 14 Mar 2026 | Originally published
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