Drug interactions
Ferrous sulfate + Levothyroxine
Severity: Moderate
Ferrous sulfate 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 sulfate forms poorly absorbed complexes with levothyroxine in the gut, lowering thyroid hormone exposure. Raised TSH and hypothyroid symptoms have been documented in patients taking both.
What this interaction means in plain words
Ferrous sulfate 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 sulfate 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 ferrous sulfate by at least 4 hours. Check TSH 6 to 8 weeks after starting or stopping iron and adjust the levothyroxine dose if needed.
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?
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Other interactions of Levothyroxine
Other interactions of Ferrous sulfate
Frequently asked questions
Can I take Ferrous sulfate with Levothyroxine?
MediHelp rates the interaction as moderate. Ferrous sulfate 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 sulfate forms poorly absorbed complexes with levothyroxine in the gut, lowering thyroid hormone exposure. Raised TSH and hypothyroid symptoms have been documented in patients taking both.
How serious is the interaction between Ferrous sulfate 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 ferrous sulfate by at least 4 hours. Check TSH 6 to 8 weeks after starting or stopping iron and adjust the levothyroxine dose if needed.
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.
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