Can You Take Iron and Levothyroxine Together?

Iron can reduce how much levothyroxine your body absorbs -- FDA labeling recommends spacing them at least 4 hours apart.

Use cautionEvidence: High

See the full Iron page and Levothyroxine page for other reviewed interactions and reference information.

What the interaction means

Levothyroxine's FDA prescribing information lists iron among the agents that may decrease absorption of the medication: "Calcium carbonate may form an insoluble chelate with levothyroxine, and ferrous sulfate likely forms a ferric-thyroxine complex. Administer levothyroxine at least 4 hours apart from these agents." The label's patient information section states plainly: "Agents such as iron and calcium supplements and antacids can decrease the absorption of levothyroxine sodium tablets... should not be administered within 4 hrs of these agents."

Why it may happen

Ferrous sulfate likely forms a ferric-thyroxine complex with levothyroxine in the gastrointestinal tract, reducing how much of the medication is absorbed into the bloodstream.

Practical context

This is the same class of absorption interaction already documented for calcium and levothyroxine on this site, reflected directly in levothyroxine's FDA labeling rather than an emerging or uncertain finding.

Timing

A spacing interval of about 240 minutes is documented in the sources below.

What the sources say

Levothyroxine Sodium Tablets — FDA Prescribing Information — via DailyMed, U.S. National Library of Medicine

Last reviewed 2026-08-22

Medical information disclaimer: this information is general and educational. It does not diagnose conditions, prescribe treatment, or determine whether a combination is safe for you personally. Follow your prescription label and ask a pharmacist or clinician before starting, stopping, or combining products. Full disclaimer.