Does iron interact with any medications?

Iron supplements can reduce the effectiveness of levothyroxine, and labels advise not taking them within 4 hours of each other.

What this means for you

One interaction matters more than the rest, and it is easy to get right once you know it.

Iron supplements reduce how well levothyroxine works, and the label says to keep the two at least four hours apart. In practice that usually means the thyroid tablet on waking and the iron at lunch or in the evening. If you have been taking both together and your thyroid numbers look unstable, this is worth mentioning at your next appointment.

The same four-hour habit is a sensible default for other things iron competes with, including calcium supplements and antacids. Tea and coffee also reduce iron absorption, which is not a drug interaction but has the same practical shape: separate them by an hour and the problem goes away.

None of this applies to iron in food. Nobody needs to schedule a steak.

Food counts as an interaction here too, and it is the one people control most easily. Tea, coffee, milk and calcium supplements taken with an iron tablet cut how much gets in, while vitamin C in the same meal pushes the other way. All of that applies to the non-heme iron in plants and fortified foods, which is the form most affected by what sits beside it on the table.

Bread is the underrated half of that. Phytate in wholemeal grain holds iron back, and in the two hours after a meal a low-phytate white loaf doubled the rise in blood iron against a high-phytate wholemeal one. Add the enzyme that breaks phytate down and absorption of a ferrous sulfate dose rose by about half. So a tablet swallowed with a wholemeal sandwich is not the neutral act it looks like.

Unsettled. The vitamin C half of that is on softer ground than the rest. Trials that added vitamin C rich fruit to meals lifted ferritin by about 9 micrograms per litre and haemoglobin by about 1.3 g/L, and left measured absorption exactly where it was. The tea and coffee effect is the better established of the two.

Written from the evidence cards and the data on this page, then checked back against the sources. Bioma Learn has no human medical reviewer at this time and we say so rather than invent one. Information, not medical advice. How we verify.

Full guide: Iron: why the number on the label is not the number your body gets