Yes, in some patients medical marijuana can control seizures.

Also called medical cannabis, it is derived from the whole cannabis plant or consists of chemicals in the plant and is used for medicinal purposes. Cannabinoids are substances in cannabis that act on cells in the body, including the brain. Two main ones are tetrahydrocannabinol (THC) and cannabidiol (CBD).

THC is the major chemical compound found in many strains of marijuana. When it binds to receptors in the brain, it creates the high that people feel, which is considered a psychoactive effect. CBD is not psychoactive and cannot create a high.

Epidiolex, a mostly purified plant-based cannabidiol oil, was approved by the US Food and Drug Administration (FDA) in 2018 to treat seizures in people with Dravet syndrome and Lennox-Gastaut syndrome, two rare forms of childhood-onset epilepsy. In 2020, Epidiolex was approved to treat seizures caused by tuberous sclerosis complex, a rare genetic disease that causes benign tumors to grow in the brain—which can lead to seizures—and other areas. The drug is a liquid that's administered orally with a special syringe.

Approval of Epidiolex for Lennox-Gastaut and Dravet syndromes was based on four randomized, double-blind, placebo-controlled clinical trials of 516 patients. Taken with other antiseizure medications, Epidiolex significantly reduced the number of seizures compared with the placebo. In a clinical trial for people with seizures caused by tuberous sclerosis complex, Epidiolex reduced seizures by 48 percent, versus 24 percent for the placebo. Since its approval, the drug has helped many people with these types of seizures, but it is not effective for everyone and may need to be discontinued due to side effects such as liver problems and suicidal thoughts.

Researchers are not clear how CBD works to treat seizures, but they have a few theories: It may slow the sending of messages to the brain, change calcium levels in the brain that affect signals between cells, or reduce inflammation in the brain.

Marijuana products sold in dispensaries and online are not approved or regulated by the FDA and can vary significantly in quality. No government agency regularly tests such products for safety or effectiveness, or verifies that what is listed on the label is actually in the product. In some cases, commercial, nonprescription cannabis products are thought to increase seizures.

Researchers continue to investigate the different chemical compounds in marijuana and how they may help treat neurologic diseases, including other types of epilepsy. A meta-analysis published in Epilepsia in 2020 found that CBD improved the effect of clobazam (Onfi), a benzodiazepine used as an add-on treatment for seizures in both children and adults who have Lennox-Gastaut syndrome. A study published in Epilepsy & Behavior in 2018 showed that Epidiolex reduced seizures associated with four other types of epilepsy—CDKL5 deficiency disorder, Aicardi syndrome, Doose syndrome, and dup15q syndrome—from an average of 59 a month to 22 a month. The improvement lasted the entire 48 weeks of the study.

Side effects observed during the clinical trials of Epidiolex include fatigue, nausea, and diarrhea. Some patients experienced elevated liver enzymes, most likely because CBD is broken down in the liver. Because of that, patients need their liver enzymes monitored while taking Epidiolex or any other medical cannabis product.

In patients whose seizures are uncontrolled—which is the case for roughly 30 percent of people with epilepsy—an FDA-approved CBD product may be an appropriate treatment. That decision should be reached after a thorough evaluation at a specialized epilepsy center of the effectiveness of all other possible treatments (including FDA-approved new and add-on medicines, dietary therapy, devices, and surgery). If doctors prescribe Epidiolex, they must monitor patients' enzyme levels and watch for any interactions with other medications.

Dr. Patel is director of the Complex Epilepsy Clinic and associate medical director for quality improvement at Nationwide Children’s Hospital in Columbus, OH. He is also associate professor of clinical pediatrics and neurology at the Ohio State University College of Medicine.