Cannabis has arguably become the most popular recreational drug in the U.S. in recent years—with more Americans now consuming it daily than cigarette smoking and even alcohol. Research out today highlights a possible dark side to frequent cannabis use for at least some people, however: a greater risk of worsening seizures.
Researchers at the Washington University School of Medicine in St. Louis studied people with treatment-resistant epilepsy, and found that people who reported frequent cannabis use were more likely to have severe seizures, while the progression to severe epilepsy was significantly faster in this group as well. The results, while not firm proof of a causative connection, merit more study and potential caution surrounding cannabis among those with epilepsy, the researchers say.
“These findings highlight the need for clinical screening and prospective studies to evaluate the impact of cannabis on seizure outcomes,” the researchers wrote in their paper, published Monday in the journal Epilepsia.
The cannabis effect?
The researchers were motivated to conduct this research by their and other colleagues’ experiences in the clinic. They’ve started to see an increasing number of patients with severe epilepsy who seemed to have little else in common besides frequent cannabis use. It made them curious enough to dig deeper.
The team examined the medical records of people with drug-resistant epilepsy, meaning their condition had failed to respond to at least two anti-seizure medications. They specifically looked at people who entered an epilepsy monitoring unit at the University of Wisconsin School of Medicine and Public Health between 2019 and 2024 (several of the study’s authors had previously worked there). These inpatient units are used to evaluate people with stubborn cases of epilepsy under close supervision to determine the best course of treatment.
All told, they studied 64 patients. Twenty-two people reported frequent cannabis use, defined as using the drug at least 20 times a month, and the researchers compared them to 42 non-users.
Frequent cannabis users were more likely to have epilepsy with focal to bilateral tonic–clonic seizures, a severe type of seizure, than non-users (90% compared to 57%). They also had these severe seizures more often, and were taking more anti-seizure medications on average. And it took less time for these patients to need specialized care than non-users—a sign their condition had worsened quicker. On average, frequent cannabis users were admitted to the unit five years after the onset of their epilepsy, compared to 18 years for non-users.
What should this mean for epilepsy patients?
This study is observational, meaning it cannot demonstrate a clear cause-and-effect link between cannabis use and epilepsy. It’s also based on a small sample of patients who self-reported their level of cannabis consumption, further weakening conclusions that can be drawn from the data. At the same time, the authors say there’s enough worrying evidence to warrant further research into the topic.
There’s actually a FDA-approved treatment derived from cannabis—Epidiolex—used to manage certain kinds of seizure. Importantly, though, Epidiolex is only made from cannabidiol (CBD), one of the two major active compounds in cannabis and not the other, THC. And the team strongly suspects THC could be the primary culprit behind this unsettling trend.
The researchers note that today’s recreational cannabis contains much more THC on average than products did in the past. There is some evidence, according to the authors, that chronic high THC use could change brain signaling, particularly in the hippocampus, ways that make severe temporal lobe epilepsy more likely to happen.
“Essentially THC can remove the brakes in the hippocampus which may result in seizures,” senior study author Aaron Struck, an adult epileptologist at WashU Medicine, told Gizmodo.
THC might also weaken the effectiveness of anti-seizure medications, the researchers argue, and people who use cannabis all the time might also be more likely to forget taking their medications as often, offering another possible explanation.
The study also found people who first reported using cannabis in the past decade were quicker to develop seizures afterward than those who started two or more decades ago. That’s perhaps another clue that higher THC products today are to blame for this recent trend, though this finding should be viewed with caution for now due to the small number of people and the use of self-reports, the researchers wrote. That said, other studies have pointed to a greater risk of health problems linked to high THC cannabis, including changes to the brain.
The team is now working on a larger, more proactive study that will look at a greater diversity of people with epilepsy, including from areas of the country with different patterns of cannabis legalization. They also plan to objectively measure people’s cannabis use, such as through blood tests for THC.
For the time being, there are still more questions than answers about the link between cannabis and epilepsy. But it might already be prudent for people with epilepsy risk to moderate their cannabis use, Struck said.
“The primary take away is to not ignore cannabis use in epilepsy or to assume it is beneficial,” he said. “It is worthwhile to discuss with a treating physician if stopping or reducing THC may be beneficial to your care. If it is being used for pain, insomnia, anxiety/depression is may be worthwhile to consider alternative therapies both pharmacological or behavioral such as meditation or exercise.”
This article has been updated with comments from one of the study’s authors.
