More Support for Causal Link Between Marijuana and Stroke

Megan Brooks

February 20, 2015

A systematic appraisal of published case reports supports a causal link between smoking marijuana and cerebrovascular events, new research suggests.

"An increasing number of case reports link cannabis consumption to cerebrovascular events. Yet these case reports have not been scrutinized using criteria for causal inference," explains Daniel G. Hackam, MD, PhD, Division of Clinical Pharmacology, Western University, London, Ontario, Canada.

He reviewed 34 case reports or case series of cannabis and cerebrovascular events in 64 stroke patients (80% men; mean age, 32 years). Most infarctions occurred in the anterior circulation (56%); 3 cases involved both anterior and posterior circulations (5%); and the remainder occurred in the posterior circulation (36%) or were not classified (3%).

Dr Hackam applied four causality criteria: temporality, adequacy of stroke work-up, effects of rechallenge, and concomitant risk factors that could account for the cerebrovascular event.

In a report online February 19 in Stroke, he reports that 81% of cases exhibited a temporal relationship with cannabis use and the index event; the patient sustained a stroke within 24 hours of using cannabis.

"In 70%, the evaluation was sufficiently comprehensive to exclude other sources for stroke," Dr Hackam reports.

Nearly a quarter (22%) of patients had another stroke after subsequent re-exposure to cannabis. Half of patients had risk factors for stroke, most commonly tobacco use (34%) and alcohol (11%) consumption. Forty-eight of the 64 patients underwent toxicologic analysis for common street drugs, and results were positive for drugs other than marijuana in only two cases.

These findings align "well with epidemiological and mechanistic research on the cerebrovascular effects of cannabis," Dr Hackam notes in his article.

He says it's "striking" that more strokes are not seen given the broad use of marijuana by the general public. This could be due to variations in dosage, frequency of use, strength of marijuana (percentage of tetrahydrocannabinol), genetic susceptibility, and other drugs used with marijuana.

"It is possible that exposure is not mentioned by patients with stroke in emergency departments, or that such exposure is overlooked. Overall, however, it seems clear that physiological, clinical, and epidemiological data converge on an increased stroke risk from cannabis exposure," Dr Hackam says.

"Heightened clinician awareness of this association, particularly in the treatment of young adults, is necessary for preventing recurrent events from future re-exposure to cannabis," he advises.

Dr Hackam has disclosed no relevant financial relationships.

Stroke. Published online February 19, 2015. Abstract

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