Can I take magnesium with levothyroxine?
Last updated September 3, 2026.
Yes, but keep them at least 4 hours apart. Levothyroxine is easy to block: calcium, iron, antacids, and magnesium supplements bind it in the stomach so less of your dose gets absorbed. MedlinePlus says to take calcium carbonate (Tums) or iron at least 4 hours before or after levothyroxine, and the NHS lists antacids, indigestion treatments, calcium, and iron as interfering products. Magnesium is not named on the levothyroxine label, but it acts the same way, which is why pharmacists apply the same 4-hour rule. Watch out for hidden magnesium too: many multivitamins, sleep powders, and antacids contain it. A clean routine is levothyroxine with water on an empty stomach in the morning, magnesium with a later meal.
What to do
- Separate by 4 hours: levothyroxine first, magnesium (and calcium or iron) at least 4 hours later.
- Check labels: multivitamins, antacids, and laxatives often contain magnesium or calcium.
- Stay consistent: take levothyroxine the same way every day so your dose stays predictable.
- Flag blood tests: tell your doctor about supplements before thyroid checks, since biotin and minerals can skew results.
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