Medication·Interactions & depletion·Reviewed June 9, 2026
Phenytoin interactions.
Phenytoin has 8 documented interactions in the NutriStack database. Prolonged use is also associated with lower Folate, Vitamin D, Calcium, and Vitamin K. The full interaction list, depletion table, and replacement suggestions are below. None of this is a substitute for your prescriber's advice.
Phenytoin at a glance.
A quick, data-grounded summary. The full tables are below.
Phenytoin has 8 documented interactions in the NutriStack database. Prolonged use is also associated with lower Folate, Vitamin D, Calcium, and Vitamin K. The full interaction list, depletion table, and replacement suggestions are below. None of this is a substitute for your prescriber's advice.
Substances that interact with phenytoin.
Every supplement and medication in the NutriStack database with a documented interaction with this drug, highest-severity first. Open any pair for the mechanism and sources.
| Substance | Interaction | What happens |
|---|---|---|
| Carbamazepine | Caution | Both are potent CYP enzyme inducers that affect each other's metabolism. Phenytoin can decrease carbamazepine levels, while carbamazepine can... details → |
| Methylfolate | Caution | Phenytoin depletes folate levels through increased catabolism and impaired absorption, potentially causing megaloblastic anemia. However, folate... details → |
| Vitamin B9 | Caution | Phenytoin depletes folate and folate supplementation may reduce phenytoin levels. This bidirectional interaction requires careful management. details → |
| Activated Charcoal | Timing Sensitive | Activated charcoal can strongly adsorb phenytoin in the gut and reduce its absorption. In volunteer data, charcoal given immediately after phenytoin... details → |
| Calcium | Timing Sensitive | Calcium can reduce phenytoin absorption if taken simultaneously. While calcium supplementation may be important for patients on phenytoin (which... details → |
| Vitamin B12 | Synergy | Phenytoin therapy is associated with lower vitamin B12 levels and higher homocysteine in multiple studies. B12 deficiency can cause anemia,... details → |
| Vitamin B6 | Synergy | Enzyme-inducing antiseizure drugs such as phenytoin have been associated with vitamin B6 deficiency. Low B6 can contribute to neuropathy symptoms... details → |
| Vitamin D3 | Synergy | Phenytoin is a potent CYP enzyme inducer that accelerates vitamin D catabolism through increased 24-hydroxylase activity. Long-term phenytoin use... details → |
What phenytoin can deplete.
Nutrients this medication is associated with lowering over time, with the mechanism, a suggested replacement where one applies, and the biomarker to monitor. Discuss any replacement with your prescriber first.
| Nutrient | Severity | How it happens | Replace with | Monitor |
|---|---|---|---|---|
| Folate | Significant | Phenytoin impairs intestinal folate absorption and increases folate catabolism during chronic use. | Methylfolate | Serum folate or RBC folate |
| Vitamin D | Significant | Hepatic enzyme induction accelerates vitamin D catabolism, lowering active vitamin D availability and worsening bone loss. | Vitamin D3 | 25-OH vitamin D |
| Calcium | Significant | Reduced vitamin D activity and chronic anticonvulsant use lower calcium balance and bone mineral density. | Calcium | Serum calcium or bone density trend |
| Vitamin K | Moderate | Enzyme induction may lower vitamin K-dependent clotting factor support and vitamin K status in susceptible long-term users. | Vitamin K2 | Undercarboxylated osteocalcin or clinical assessment |
| Biotin | Moderate | Chronic anticonvulsant therapy can lower biotin status through increased metabolic turnover. | Vitamin B7 | Clinical assessment |
The full phenytoin profile.
Uses, typical dosing, side effects, and the cited evidence for this medication.
Common phenytoin questions.
Quick answers drawn from the tables above.
What interacts with Phenytoin?
In the NutriStack database, Phenytoin has 8 documented interactions. The most notable include Carbamazepine, Methylfolate, Vitamin B9, Activated Charcoal, and Calcium. Check any specific combination before taking it and confirm with your prescriber.
Does Phenytoin deplete any nutrients?
Phenytoin is associated with lowering Folate, Vitamin D, Calcium, Vitamin K, and Biotin with prolonged use. Useful biomarkers to monitor include Serum folate or RBC folate, 25-OH vitamin D, and Serum calcium or bone density trend. Ask your prescriber before adding any replacement supplement.
Is it safe to take Carbamazepine with Phenytoin?
NutriStack classifies the Carbamazepine and Phenytoin pairing as caution: Both are potent CYP enzyme inducers that affect each other's metabolism. Phenytoin can decrease carbamazepine levels, while carbamazepine can decrease phenytoin levels,... Monitor serum levels of both drugs closely when used together. Dose adjustments are frequently needed. Therapeutic drug monitoring is essential. Always confirm with your prescriber.
Check your whole stack
See how phenytoin fits your supplements.
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