Study finds epilepsy patients who use cannabis may increase seizures

Researchers found that epilepsy patients who use the drug most days had over twice as many convulsive seizures as nonusers.

They also became resistant to antiseizure medications quicker than nonusers of cannabis, according to the findings of the American study.

The research team examined 64 adults with drug-resistant epilepsy — defined as when two or more medications haven't controlled seizures — who were admitted to a specialized inpatient unit.

Around one-third of the patients reported using cannabis recreationally most days.

Nine out of 10 of the frequent users experienced the convulsive types of seizures most associated with injury and sudden unexpected death in epilepsy, often referred to as "grand mal" or generalized tonic-clonic seizures.

In contrast, about half of nonusers didn't experience those types of seizures.

The research team says their findings, published in the journal Epilepsia, can't establish that cannabis use worsens epilepsy, but they said there is a "concerning" association.

Study senior author Dr. Aaron Struck says the findings make cannabis use worth raising directly with patients, especially those who are using it for issues such as insomnia.

He said: "There isn't definitive data that cannabis use worsens epilepsy.

"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."

Struck, from Washington University School of Medicine in St. Louis, noted that the research was spurred by a trend he had observed treating patients with epilepsy amid the boom in recreational cannabis use in recent years.

He said: "I was seeing patients with horrible seizures, really severe epilepsy, who didn't have any of the expected risk factors.

"The one thing they had in common was frequent, high-potency cannabis use.

"It's an uncontrolled variable that was appearing more and more in my practice, and nobody had really studied it."

A purified form of cannabidiol (CBD), a chemical compound found in cannabis, is approved by the U.S. Food and Drug Administration for treating some severe forms of epilepsy.

But the medication contains no tetrahydrocannabinol (THC), the psychoactive component in cannabis.

In animal studies, CBD has been shown to suppress seizures.

But THC may do the opposite.

The cannabis sold in the recreational market is increasingly high in THC and low in CBD, according to recent studies of potency.

To explore the relationship between frequent cannabis use and epilepsy, Struck and his colleagues analyzed records from patients treated between 2019 and 2024 in an epilepsy monitoring unit at the University of Wisconsin School of Medicine and Public Health.

They compared 22 frequent recreational users — people who reported using cannabis 20 days a month or more — with 42 nonusers.

The researchers found a "clear set of features" among the frequent users — patients in their 20s, mostly male, without the usual risk factors for epilepsy, whose seizures escalated quickly from onset to admission to the epilepsy monitoring unit.

Overall, frequent cannabis users had more recurrent and more severe seizures than nonusers did.

Struck said they were seen at the inpatient epilepsy monitoring unit — an indication that their prescribed medications had stopped working to control seizures — an average of five years after their first seizure, compared with 18 years for nonusers.

And they were discharged on more antiseizure medications despite having had epilepsy for far less time.

The researchers found that among 15 frequent users whose timelines could be documented, all started using cannabis before experiencing their first seizure, weakening the likelihood that they began using cannabis in hopes of improving their epilepsy.

Struck said that such severe epilepsy usually leaves visible scarring on the hippocampus, a seahorse-shaped structure deep in the brain that is central to memory where many seizures begin.

But frequent users' brain scans looked largely normal, which indicated to the research team that something other than the usual disease process was going on.

Struck said: "THC acts on receptors densest in those same brain regions, suggesting these patients' seizures may arise from damage to how brain circuits are firing rather than from physical damage."

The team is designing a larger study, including geographic regions with distinct cannabis legalization histories and data on use patterns.

Instead of having patients report their own cannabis use, the researchers plan to incorporate objective measures at admission for a more accurate gauge of what people actually consume.

Study first author Dr. Santiago Philibert-Rosas, a researcher in Struck's lab, said: "Right now, the honest answer when a patient asks whether their cannabis use is affecting their seizures is that we're not sure."

He added: "Larger studies will help us give them a real answer — how much matters and whether stopping helps — so they can make an informed decision."