Can I take 15 and Levothyroxine together?
Drug interaction guide
Originally published 14 Mar 2026
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Taking iron supplements (like ferrous sulphate) at the same time as levothyroxine can stop your thyroid medication from working properly. The iron binds to the levothyroxine in your stomach, which means your body cannot absorb the medicine into your bloodstream. This could lead to your thyroid becoming underactive again, causing symptoms like tiredness, weight gain, and feeling cold.
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Why this happens
Iron forms a 'complex' with levothyroxine in the digestive tract. This large molecule is too big to be absorbed through the gut wall, so the levothyroxine simply passes through your system without being used.
What you should do
Back to contentsYou must space these two treatments apart. Take your levothyroxine on an empty stomach, at least 30 to 60 minutes before breakfast. Then, wait at least 4 hours before taking your iron supplement. Do not stop taking either medication without speaking to your doctor, as they may need to check your thyroid levels (TSH) with a blood test.
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Using other medicines
Back to contentsTaking 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.
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Article history
The information on this page is written and peer reviewed by qualified clinicians.
14 Mar 2026 | Originally published
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