Pauline Anderson

May 02, 2014

PHILADELPHIA — Although past case reports and other studies have suggested that using marijuana may raise the risk for stroke, a new study did not find this association and, in fact, found a statistically significant inverse relationship between marijuana use more than a year ago and ischemic stroke risk in young people.

"We don't suspect that this implicates a protective effect of marijuana on ischemic stroke risk," stressed lead researcher Tara Dutta, MD, Stroke Fellow, University of Maryland School of Medicine, Baltimore. "We will go back and look at our data more carefully and do some additional analyses to see if we can look for potential confounders."

The researchers presented their findings here at the American Academy of Neurology (AAN) 66th Annual Meeting.

Drug Use

The Stroke Prevention in Young Adults Study was a population-based case control study of young adults aged 15 to 49 years. It included 751 stroke cases and 813 age-, race-, and sex-matched control patients without a history of ischemic stroke.

Compared with control patients, the stroke cases were more likely to be men, to have a history of diabetes and hypertension, and to report current tobacco use. Control patients were more likely to report alcohol use.

Through a standardized interview process, researchers collected information on illicit drug use, including the type of drug, route of administration, frequency of use, and so on. Participants could point to information on cards so they did not have to verbally state that they used a particular drug. Patients were also reassured that their personal data was protected.

Researchers divided the patients into those who had never used marijuana (n = 501) and those who had ever used it (n = 312). Ever-users were more likely than never-users to be men (48.7% vs 37.7%) and to be white (62.8% vs 52.7%), and they were slightly more likely to have hypertension.

They were significantly more likely to report current smoking (29.5% vs 13.6%; P ˂ .001) and current alcohol use (78.9% versus 53.9% P ˂ .001).

Time of Use

The researchers also divided the users by time of marijuana use: "years ago" (defined as any use a year or longer ago, including 1-time use and recurrent use), "months ago" (any use more than a month ago), within 1 to 30 days, and within 24 hours.

The data did not show evidence for an increased risk for ischemic stroke associated with marijuana use when adjusted for age, sex, race, current tobacco smoking and alcohol use, hypertension, and diabetes.

Dr. Dutta pointed out, however, that the numbers got quite small in the groups using the drug within the last 30 days. For example, 2.8% of stroke cases and 2.7% of control patients reported using marijuana within the previous 30 days, and only 0.9% of stroke cases and 0.7% of control patients reported use within the last 24 hours.

Inverse Relationship

However, among those reporting using marijuana "years ago," there was an inverse relationship between marijuana use and ischemic stroke risk. The study showed that 28.8% of stroke patients reported using marijuana "years ago" compared with 32.7% of control patients (odds ratio adjusted for current tobacco use and other risk factors, 0.77; 95% confidence interval [CI], 0.61 - 0.98; P = .03).

After Dr. Dutta's presentation, Alan Barber, MD, a stroke neurologist and professor, clinical neurology, University of Auckland, New Zealand, who has also studied stroke risk and marijuana use, pointed out the accuracy issues associated with self-reporting of illicit drug use.

In his own study, presented at the International Stroke Conference 2013 and reported by Medscape Medical News at that time, the researchers found an increased risk for stroke associated with marijuana use in a case-control study. However, he indicated here that he had found it difficult to "tease out" tobacco use from other drug use, as all but 1 of his stroke patients who used cannabis also smoked tobacco.

Speaking to Medscape Medical News, session cochair Lori Billinghurst, MD, from Children's Hospital of Philadelphia, said that despite the new study results, it is unlikely there is a protective effect from remote marijuana use.

"That's probably not really borne out with this data, as it was a very small sample size," she said. "The question is still out there, the research still needs to be done. Patients are interested, and I think this lays a foundation for that."

Probing the question further is even more important now that an increasing number of states allow residents to use marijuana recreationally. "From a population health perspective, we really need more data to know what marijuana is doing," said Dr. Billinghurst.

Widespread Effects

In an interview, Dr. Dutta added that it is important for physicians to stress to patients that marijuana is a drug and that just like any drug, it may have "widespread effects" on the cerebrovascular and other systems throughout the body that are not fully understood.

Patients often assume that because it is a plant derivative, marijuana is harmless, said Dr. Dutta. "People have to understand that marijuana as smoked on the street contains a variety of other chemicals. It often contains tobacco and can be cut with other substances, which can be chemical adulterants, amphetamine derivatives which may increase stroke risk independently or have an additive effect."

Still, Baby Boomers who smoked marijuana, sometimes extensively, during the 1960s and 1970s, do not appear to be suffering any health effects. Dr. Dutta pointed out that the concentration of tetrahydrocannabinol in marijuana on the street today is much higher than it used to be.

Future studies will look into the effect of frequent or heavy marijuana use and the identification of potential genetic modifiers of marijuana risk, said Dr. Dutta.

Marijuana is the most commonly used drug in the United States and worldwide, and its use is increasing, particularly in teenagers and young adults

Dr. Dutta has disclosed no relevant financial relationships.

American Academy of Neurology (AAN) 66th Annual Meeting: Abstract S55.003. Presented May 1, 2014.

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