Drug interactions
Ferrous fumarate + Levothyroxine
Severity: Moderate
Ferrous fumarate and Levothyroxine: moderate interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Ferrous iron binds levothyroxine in the gut, lowering its absorption. Patients may develop a higher TSH and symptoms of hypothyroidism despite a stable dose.
What this interaction means in plain words
Ferrous fumarate and Levothyroxine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Ferrous fumarate belongs to Miscellaneous; Levothyroxine belongs to Endocrine.
Why it happens
Iron chelates levothyroxine in the gastrointestinal tract, reducing its absorption.
What to do
Separate levothyroxine and iron by at least 4 hours. Check TSH 6 to 8 weeks after starting or stopping iron.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
Pro+ members
Unlock the full page
Create an account and start a Pro+ trial to unlock the full management advice for Ferrous fumarate and Levothyroxine, the additional notes, the evidence detail and the whole-prescription interaction checker.
- Full clinical management advice
- Additional notes
- Evidence detail
- Interaction checker for a whole prescription
Try Pro+ free for 14 days on the web. No card needed.
Other interactions of Levothyroxine
Other interactions of Ferrous fumarate
Frequently asked questions
Can I take Ferrous fumarate with Levothyroxine?
MediHelp rates the interaction as moderate. Ferrous fumarate and Levothyroxine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Ferrous iron binds levothyroxine in the gut, lowering its absorption. Patients may develop a higher TSH and symptoms of hypothyroidism despite a stable dose.
How serious is the interaction between Ferrous fumarate and Levothyroxine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Separate levothyroxine and iron by at least 4 hours. Check TSH 6 to 8 weeks after starting or stopping iron.
What other medicines interact with Levothyroxine?
MediHelp also lists interactions of Levothyroxine with, for example, Cholestyramine, Sodium iodide i-131, Tiratricol. The full list is on the Levothyroxine page.
Full monographs, dosing and an interaction checker in the MediHelp app
Open the complete reference, check multi-drug interactions and use dosing tools in the MediHelp app.
