Drug interactions
Carbonyl iron + Levothyroxine
Severity: Moderate
Carbonyl iron 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
Iron forms insoluble complexes with levothyroxine in the gut, reducing its absorption. This can cause rising TSH and hypothyroid symptoms in patients who take the two together.
What this interaction means in plain words
Carbonyl iron 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.
Carbonyl iron belongs to Miscellaneous; Levothyroxine belongs to Endocrine.
Why it happens
Iron chelates levothyroxine in the gastrointestinal tract and impairs its absorption.
What to do
Give levothyroxine at least 4 hours before or after iron. Check TSH 6 to 8 weeks after iron is started or stopped.
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 Carbonyl iron 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 7 days on the web. No card needed.
Other interactions of Levothyroxine
Other interactions of Carbonyl iron
- Aluminum hydroxide + Carbonyl iron Moderate
- Baloxavir marboxil + Carbonyl iron Moderate
- Calcium acetate + Carbonyl iron Moderate
- Calcium carbonate + Carbonyl iron Moderate
- Calcium + Carbonyl iron Moderate
- Carbidopa-entacapone-levodopa + Carbonyl iron Moderate
Frequently asked questions
Can I take Carbonyl iron with Levothyroxine?
MediHelp rates the interaction as moderate. Carbonyl iron 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. Iron forms insoluble complexes with levothyroxine in the gut, reducing its absorption. This can cause rising TSH and hypothyroid symptoms in patients who take the two together.
How serious is the interaction between Carbonyl iron 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: Give levothyroxine at least 4 hours before or after iron. Check TSH 6 to 8 weeks after iron is started or stopped.
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.
