Levothyroxine and Carbamazepine Interaction
Drug interaction information between Levothyroxine and Carbamazepine.
Levothyroxine and Carbamazepine have a documented minor interaction in FDA labeling.
FDA drug labeling documents a minor-severity interaction between Levothyroxine and Carbamazepine. Major interactions are generally avoided, moderate ones may need monitoring or a dose adjustment, and minor ones are usually low-risk. This page shows the documented mechanism and guidance. Label-documented interactions are not a complete safety review, so always confirm your own medications with a pharmacist or doctor. Educational information, not medical advice.
How They Interact
Carbamazepine changes how thyroid hormone travels in your blood, which can lower the levels of hormone found in medical tests.
What To Do
Your doctor may need to check your thyroid levels and adjust your dose if you start or stop taking this medication.
FDA Label Information
Other drugs: Carbamazepine Furosemide (> 80 mg IV) Heparin Hydantoins Non-Steroidal Anti-inflammatory Drugs - Fenamates These drugs may cause protein-binding site displacement. Phenytoin and carbamazepine reduce serum protein binding of levothyroxine, and total and free T4 may be reduced by 20% to 40%, but most patients have normal serum TSH levels and are clinically euthyroid. Other drugs: Carbamazepine Furosemide (> 80 mg IV) Heparin Hydantoins Non-Steroidal Anti-inflammatory Drugs - Fenamates These drugs may cause protein-binding site displacement.
Levothyroxine Also Interacts With
- Sertraline minor
- Furosemide minor
- Propranolol minor
- Ferrous Sulfate minor
- Amitriptyline minor
Carbamazepine Also Interacts With
- Nirmatrelvir/Ritonavir major
- Ranolazine major
- Risperidone major
- Lithium moderate
- Apixaban moderate
Frequently Asked Questions
Can I take Levothyroxine and Carbamazepine together?
This is a minor interaction. Your doctor may need to check your thyroid levels and adjust your dose if you start or stop taking this medication.
How serious is the interaction between Levothyroxine and Carbamazepine?
This interaction is classified as "minor" severity by the FDA. Minor interactions are unlikely to cause significant problems but should still be mentioned to your healthcare provider.
Why do Levothyroxine and Carbamazepine interact?
Carbamazepine changes how thyroid hormone travels in your blood, which can lower the levels of hormone found in medical tests.
Understanding the Levothyroxine and Carbamazepine Interaction
FDA-approved prescribing information for these two drugs flags their combination as a minor-severity interaction. Levothyroxine belongs to the Thyroid Hormone class and Carbamazepine belongs to the Anticonvulsant class - two categories that can collide when co-prescribed. The mechanism described in FDA labeling is: Carbamazepine changes how thyroid hormone travels in your blood, which can lower the levels of hormone found in medical tests. Severity tiers matter: major flags generally advise avoidance, moderate flags often require monitoring or dose adjustment, and minor flags may only call for awareness.
Context around a specific patient determines real-world impact. Levothyroxine has 22 total documented interactions on file in this dataset, and Carbamazepine has 129. Each additional medication compounds the interaction surface, which is why pharmacists run full-profile checks rather than evaluating one pair at a time. FDA-derived guidance for this pair is: Your doctor may need to check your thyroid levels and adjust your dose if you start or stop taking this medication. Timing of doses, renal and hepatic function, age, and other concurrent prescriptions all shape whether a labeled interaction matters clinically.
An interaction flag is not a verdict. A large share of labeled interactions are managed routinely in clinical practice, the fix may be as simple as spacing doses or adding a monitoring test. Others require the prescriber to choose a different medication entirely. This page surfaces FDA-sourced labeling and openFDA data for educational purposes only; it is not medical advice and cannot account for your full clinical picture. Never start, stop, or adjust either Levothyroxine or Carbamazepine based on a web page, speak with your prescriber or pharmacist before making any change.
Sources: FDA Drug Labels (SPL) via openFDA (2026). This is for informational purposes only and is not medical advice. Always consult your healthcare provider about drug interactions.
Read our methodology - how this data is sourced, computed, and verified.