Drug interactions
Levothyroxine + Warfarin
Severity: Moderate
Levothyroxine and Warfarin: 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
Levothyroxine increases warfarin sensitivity, so the INR can rise once thyroid hormone replacement is started or the dose is increased. The reverse occurs when the dose is reduced.
What this interaction means in plain words
Levothyroxine and Warfarin 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.
Levothyroxine belongs to Endocrine; Warfarin belongs to Cardiovascular.
Why it happens
Thyroid hormone increases catabolism of vitamin K-dependent clotting factors, enhancing warfarin's effect.
What to do
Check INR frequently after starting or changing the levothyroxine dose and reduce warfarin as 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 Warfarin
- Defibrotide + Warfarin Contraindicated
- Ketorolac + Warfarin Contraindicated
- Abciximab + Warfarin Major
- Acetylsalicylic acid + Warfarin Major
- Adagrasib + Warfarin Major
- Amiodarone + Warfarin Major
Other interactions of Levothyroxine
Frequently asked questions
Can I take Levothyroxine with Warfarin?
MediHelp rates the interaction as moderate. Levothyroxine and Warfarin 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. Levothyroxine increases warfarin sensitivity, so the INR can rise once thyroid hormone replacement is started or the dose is increased. The reverse occurs when the dose is reduced.
How serious is the interaction between Levothyroxine and Warfarin?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Check INR frequently after starting or changing the levothyroxine dose and reduce warfarin as needed.
What other medicines interact with Warfarin?
MediHelp also lists interactions of Warfarin with, for example, Defibrotide, Ketorolac, Abciximab. The full list is on the Warfarin page.
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