Phenytoin

For an informed discussion with your doctor or pharmacist. This information collection is not a clinically validated interaction checker. Missing data do not establish safety. Do not change or stop prescribed medicines on the basis of this information. The findings apply to the specific conditions studied; laboratory and animal studies cannot be directly extrapolated to humans.

Active substance: Phenytoin

Examples of brand names: Phenhydan [DE]

ATC code: N03AB02

Main use (for orientation): Epilepsy

Documented research summary

Two CBD cases reported in 2026 with increased phenytoin concentrations/reduced clearance, one involving ataxia/falls. The null finding in the smaller phenytoin subgroup in CL20 is retained as contrary evidence.

Uncertainties and limitations

Case reports do not establish an average magnitude; quantitative doses/concentrations were unavailable in the abstract read. PMID15210913 without an accessible abstract/full text; metadata alone do not permit inference of an effect. Historical combination case PMID808653 also involves phenobarbital; not isolated phenytoin pharmacokinetics.

Separately recorded findings

1 separately recorded finding. Each statement applies to its documented study context.

CBD – clinical signals

Finding ID: B0069

Type of result: No / minor effect under the conditions studied

Observation: No concentration signal; p=0.6529.

Mechanism: PK observation

Study type: Observational study: no signal detected

Context studied: n=11.

Clinical interpretation: Not ruled out

Limitations and uncertainties: Context / limitations of CL20; a lack of statistical significance does not establish equivalence.

Original sources for this finding: Final analysis of potential drug-drug interactions between highly purified cannabidiol and anti-seizure medications in an open-label expanded access program [CL20]

References and access status

[CA_L_D0044] EXTENDED PHENYTOIN SODIUM (PHENYTOIN SODIUM) CAPSULE [REMEDYREPACK INC.]

Original source / bibliographic reference

Authors: REMEDYREPACK INC.

Year: 2026

Source type: Current published human-use SPL / product information

Source access – 23 October 2026: Source destination was accessible when checked.

Bibliographic attribution or source identity cross-checked.

[CL20] Final analysis of potential drug-drug interactions between highly purified cannabidiol and anti-seizure medications in an open-label expanded access program

Original source / bibliographic reference

Authors: Gaston TE; Bebin EM; Cutter GR; Grayson L; Szaflarski JP

Year: 2023

Source type: Open-label longitudinal observational study

DOI: 10.1002/epi4.12815

PMID: 37593907

Source access – 23 October 2026: Automated direct retrieval was restricted; this does not establish that the link is broken.

Bibliographic attribution or source identity cross-checked.

PubMed – bibliographic reference / abstract

DOI – publisher access (access restrictions may apply)

Europe PMC – full-text access according to the literature database – Listed as freely available HTML full text in the official Europe PMC metadata. Direct retrieval was not fully verified here.

[CA_P_41764811] Cannabidiol inhibits phenytoin clearance and can result in clinical changes: Two cases.

Original source / bibliographic reference

Authors: Blond BN, Cardoza C, Mattson RH.

Year: 2026

Source type: Journal Article; Case Reports

DOI: 10.1016/j.seizure.2026.02.019

PMID: 41764811

Source access – 23 October 2026: Direct retrieval could not be fully verified; availability remains unresolved.

Bibliographic attribution or source identity cross-checked.

DOI – publisher access (access restrictions may apply)

[CA_P_15210913] Recreational use of phenytoin, marijuana, and alcohol: a case report.

Original source / bibliographic reference

Authors: Jessen K.

Year: 2004

Source type: Journal Article; Case Reports

DOI: 10.1212/01.wnl.0000130334.79514.ea

PMID: 15210913

Source access – 23 October 2026: Automated direct retrieval was restricted; this does not establish that the link is broken.

Bibliographic attribution or source identity cross-checked.

DOI – publisher access (access restrictions may apply)

[CA_P_808653] Anticonvulsant nature of marihuana smoking.

Original source / bibliographic reference

Authors: Consroe PF, Wood GC, Buchsbaum H.

Year: 1975

Source type: Research Support, U.S. Gov't, Non-P.H.S.; Journal Article; Case Reports

DOI: 10.1001/jama.1975.03260160054015

PMID: 808653

Source access – 23 October 2026: Source destination was accessible when checked.

Bibliographic attribution or source identity cross-checked.

DOI – publisher access (access restrictions may apply)

Research as of 23 October 2026. Not all original full texts could be reviewed in full. Source accessibility and the strength of scientific evidence must be assessed separately. An accessible link does not establish medical approval; a bibliographic record with an abstract does not replace the original full text.

Drug search and explanation of the evidence · Guide: cannabinoids and medicines · Author and responsibility