Regular cannabis use tied to more severe epilepsy

Clinical takeaway: Ask patients with epilepsy about cannabis use, especially those using it most days. Near-daily use tracked with a more severe course, and patients using cannabis for sleep or anxiety have better-proven options. 

Patients with epilepsy use cannabis for sleep, for anxiety, and sometimes in the hope of calming seizures themselves. At the same time, the recreational cannabis market has shifted toward products with higher levels of tetrahydrocannabinol (THC) and lower levels of cannabidiol (CBD). By 2022, US adults reporting daily or near-daily cannabis use outnumbered those reporting comparable alcohol use.

Purified CBD is FDA-approved for treating seizures in specific severe epilepsies, while animal studies suggest THC may increase seizure activity. Clinical evidence on frequent cannabis use is limited, and much of it predates today's high-THC products. A retrospective comparison of near-daily users and nonusers evaluated at a specialized epilepsy center now offers some insight.

Frequent cannabis users were evaluated in an epilepsy monitoring unit an average of 5 years after their first seizure, compared with 18 years for nonusers, suggesting a more rapid progression to medication-resistant epilepsy. They also were more likely to experience focal to bilateral tonic-clonic seizures, the seizure type most strongly associated with injury and sudden unexpected death in epilepsy (91% vs 57%), and had more than twice as many convulsive seizures per year.

Although the groups were taking similar numbers of antiseizure medications at admission, frequent cannabis users were discharged on more medications, reflecting treatment escalation during their stay. Yet brain imaging told a different story: users showed no greater loss of brain volume and were no more likely than nonusers to have the hippocampal scarring typically seen in severe temporal lobe epilepsy.

The data suggest that cannabis use was unlikely to be a response to severe epilepsy. In every frequent user with a documented timeline, cannabis use began before the onset of seizures.

Researchers at the University of Wisconsin–Madison reviewed records from 64 adults with drug-resistant focal epilepsy admitted to the center's epilepsy monitoring unit between 2019 and 2024, comparing 22 patients with documented cannabis use on 20 or more days per month versus 42 with no documented use. Cannabis exposure came from the medical record rather than a standardized instrument, and occasional users were excluded. 

The team is designing a larger, multisite study spanning regions with different legalization histories, and it plans to replace self-report with objective cannabis measures at admission. Those measures would answer what this study cannot, which is how much use matters and whether stopping helps. 

"There isn't definitive data that cannabis use worsens epilepsy," said Aaron F. Struck, MD, an associate professor of neurology at WashU Medicine and senior author of the study. "But if someone is using cannabis to help with anxiety or sleep, I'd prefer to treat those problems with drugs we understand rather than something largely unregulated whose impact on the brain we don't really know." 

Source: Philibert-Rosas S, et al. (2026 Sep 28) Epilepsia. Frequent cannabis use and the association with seizure burden in drug-resistant epilepsy