It is possible smoking marijuana can cause seizures under certain circumstances, but current data doesn't provide sufficient proof. A few human reports or animal studies suggest marijuana or its cannabinoids can cause seizure activity, but other studies suggest they are also protective against seizures. Perhaps smoking weed can cause the onset of new seizures or provoke your seizure disorder if you have other factors present.
Marijuana and Seizures
The limited available data suggests marijuana may initiate seizures in some susceptible people and suppress them in others. Risk factors, such as cardiovascular disease or an underlying seizure disorder, might make you more vulnerable.
- A case report published in the Pan African Medical Journal in 2014 concluded 26-year heavy use of marijuana by a 44-year-old man caused his new onset seizures. Based on a brain MRI scan, the authors felt the seizures were provoked by a stroke brought on by the cardiovascular effects of marijuana, or the toxic effects of high and prolonged doses of weed on the brain.
- In a case of a 20-year-old man with a history of a major disorder who had been free of any seizures for six months, it was reported he had three major seizures after smoking marijuana seven times in three weeks. However, the seizures did not occur during smoking or shortly after, so the connection is uncertain.
- A survey of 310 patients in an outpatient epilepsy clinic reported in the European Journal of Neurology showed 84% of cannabis users reported no increase in seizures, while 80% of users of other drugs reported they had more seizures.
- An early human study on illicit drugs and marijuana use and the risk of new onset seizures was published in 1992 in the Transactions of the American Clinical and Climatological Association. The authors concluded marijuana was protective rather than a risk for seizures. A study group of 308 patients admitted to the hospital because of new onset seizures were compared to a control group of 294 patients admitted for surgery. Men in the study group used marijuana less frequently than those in the control group. This difference was smaller among the women. Heroin was found to be a risk factor for seizures.
The risk of inducing seizures might depend on how many joints you smoke and how frequently you smoke them, or whether you use other substances like alcohol, which make you more susceptible to seizures.
Marijuana Source, Cannabinoids, and Seizures
Each type or crop of marijuana (cannabis) plant, and therefore what you buy, may have different ratios of cannabinoids, its main chemicals. It is possible your risk for seizures from smoking pot depends on your batch of marijuana and its cannabinoid content, as well as whether it is contaminated by other illicit substances that can cause seizures, such as heroin.
The Cannabinoid Studies
Rather than the cannabis plant, most studies on seizures have looked at the effect of the two predominant cannabinoids:
- Delta-9-tetrahydrocannabinol (THC), the principal psychoactive component, which causes the euphoric high of the weed
- Cannabidiol (CBD), which has no psychoactive effect
According to a review on alcohol, marijuana, and seizures published in 2001 in the journal Epilepsia, animal studies that look at the effect of THC and CBD on seizure activity show conflicting results and depend on the animal model, the cannabinoid, and the dose used:
- One experiment reported in Neuropharmacology found a single dose of THC facilitated electrically-provoked seizures in a mouse model.
- In a followup study, the same researchers, reporting in Neuropharmacology, found susceptibility to electrically-induced seizures increased when the dose of THC was increased. In addition, this susceptibility continued up to 196 hours after a single dose of THC.
- An early study in mice published in Psychopharmacologia found THC decreased susceptibility to seizures.
- In a rat model of an epilepsy experiment reported in Epilepsia in 2007, THC excited a seizure focus in the brain and caused visible seizures. CBD did not have this effect.
- CBD, as reviewed in a study in the Journal of Pharmacology and Experimental Therapeutics, appears to be less seizure-inducing and has more anti-seizure activity than THC.
Small studies in humans also found THC may provoke seizures in some forms of inherited epilepsy but protected against most seizures.
Mechanism of Effect on Seizures
The mechanism by which marijuana or cannabinoids might either excite or reduce seizures is not clear, according to the Epilepsia review. Marijuana cannabinoids bind to cannabinoid receptors in the brain and other parts of the body. These receptors are widely distributed in the brain, including areas that control seizure activity. It is possible that whether smoking marijuana causes or prevents seizures depends on which nerve cells its cannabinoids bind to, and which neurotransmitters are activated or inhibited.
The author of a review in Biochemical Pharmacology proposes that cannabinoids might provoke seizures by binding to receptors on nerve cells that secrete the inhibitory neurotransmitters, such as gama-amino-butyric acid (GABA). A decrease in GABA would lessen its inhibition of the nerve cells it controls, leading to excitement of those cells and seizure activity. On the other hand, cannabinoids may inhibit seizures by binding to cells that inhibit the secretion of the excitatory neurotransmitter, glutamate.
The current limited evidence suggests that, under some circumstances, smoking marijuana may cause new seizures or provoke them if you have a seizure disorder. The vulnerability may persist during a period of withdrawal from the weed. Your seizure risk might be greater if you frequently smoke a lot of weed, but some people may be susceptible with less. Discuss your marijuana use with your doctor if you a have a medical condition, such as cardiovascular disease or a seizure disorder, or you use other illicit substances that might make you more vulnerable to having seizures.