ModerateThyroid hormones×Mineral supplements. Macrominerals
Updated · Methodology
Mechanism
Magnesium sits in the same label list as calcium and iron: it reduces levothyroxine absorption by binding in the gut. The effect is somewhat smaller than with calcium, but it counts when magnesium is taken daily at the same hour as the hormone, which is what happens when both live on the bedside table.
Symptoms
Mildly raised TSH across successive checks with no obvious cause and an unchanged hormone dose.
Management
Keep the 4-hour gap. Magnesium is usually taken at night for sleep and night cramps, which fits well with morning levothyroxine. No need to stop it: moving the hour is enough.
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.
Summary of a multi-drug list →
Medicine list: everything you take in one place →
Sources
- AEMPS: Ficha técnica Levotiroxina Aristo 100 microgramos comprimidos EFG (2023)– AEMPS, CIMA, nº registro 84484, sección 4.5
- NIH Office of Dietary Supplements: Magnesium – Health Professional Fact Sheet (2025)– NIH ODS, Magnesium, Interactions with Medications