Isotretinoin and Phenytoin Interaction
Drug interaction information between Isotretinoin and Phenytoin.
Isotretinoin and Phenytoin have a documented minor interaction in FDA labeling.
FDA drug labeling documents a minor-severity interaction between Isotretinoin and Phenytoin. 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
Both drugs may have an effect on bone strength, though it is not certain if taking them together increases the risk of bone loss.
What To Do
Talk to your doctor about monitoring your bone health if you need to take both of these medicines.
FDA Label Information
Phenytoin : Isotretinoin capsules have not been shown to alter the pharmacokinetics of phenytoin in a study in seven healthy volunteers. Phenytoin is known to cause osteomalacia. No formal clinical studies have been conducted to assess if there is an interactive effect on bone loss between phenytoin and isotretinoin capsules.
Isotretinoin Also Interacts With
- Progesterone major
- Retinol moderate
- Estradiol minor
- Norethindrone minor
- Minocycline minor
Phenytoin Also Interacts With
- Nirmatrelvir/Ritonavir major
- Posaconazole major
- Ranolazine major
- Voriconazole major
- Apixaban moderate
Frequently Asked Questions
Can I take Isotretinoin and Phenytoin together?
This is a minor interaction. Talk to your doctor about monitoring your bone health if you need to take both of these medicines.
How serious is the interaction between Isotretinoin and Phenytoin?
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 Isotretinoin and Phenytoin interact?
Both drugs may have an effect on bone strength, though it is not certain if taking them together increases the risk of bone loss.
Understanding the Isotretinoin and Phenytoin Interaction
FDA-approved prescribing information for these two drugs flags their combination as a minor-severity interaction. Isotretinoin belongs to the Systemic Retinoid class and Phenytoin belongs to the Anticonvulsant (Hydantoin) class - two categories that can collide when co-prescribed. The mechanism described in FDA labeling is: Both drugs may have an effect on bone strength, though it is not certain if taking them together increases the risk of bone loss. 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. Isotretinoin has 7 total documented interactions on file in this dataset, and Phenytoin has 147. 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: Talk to your doctor about monitoring your bone health if you need to take both of these medicines. 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 Isotretinoin or Phenytoin 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.