A recent study reported in the Journal of Stroke and Cerebrovascular Diseases has found that marijuana smokers have a higher rate of hospital admissions for intracerebral hemorrhages (ICH) due to stroke. Dr. Konark Malhorta and colleagues from the University of West Virginia compared very large populations (in the 10s to 100s of thousands) of nonsmokers to smokers (of cannabis) to identify risk factors for ICH. Data were obtained from 2004 to 2011. While the prevalence of ICH in smokers was higher than nonsmokers, smoking could not be determined as a predictor of ICH. That is to say, other factors such as other illicit drug use or other ICH factors could not be ruled out.
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Other smaller case studies have also suggested a causal role of smoking in ischemic stroke. Dr. Niranjan N Singh, MD, of the University of Missouri - Colombia, Missouri suggests possible mechanisms for marijuana-related stroke such as "direct effects on the cerebral circulation, orthostatic hypotension, central nervous system vasculitis, vasospasm, and atrial fibrillation". Another study of the available human literature at the time also found a positive correlation between marijuana and stroke. This was published in 2013 the Annuals of Vascular Surgery by Dr. Anne Claire Desbois at the Goupe hospitalier Pitié-Salpêtrière in France. The recommendations of all three of these studies are that more analytical assessments of the effects of marijuana on cardiovascular diseases are needed.
While the case study reports are revealing, it runs counter to what has been found in cell culture and animal studies. Dr. M. Rodrigez-Munez of the Cajal Institute in Madrid, Spain, recently found neuroprotective effects of cannabidiol (CBD; one of the many compounds found in the marijuana plant) in mice. Dr. Eugene Scharf performed a systematic review of the animal literature and concluded that "a clinical trial investigating CBD in vascular disease...would serve an immediate public health need and is a necessary next step in advancing stroke prevention".
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An often cited, although dated, paper from 1998 found neuroprotective effects in an in vitro model of stroke. Dr. Aidan Hampson and colleagues from the National Institute of Mental Health put forth that both THC and CBD may decrease the amount of damage caused by a stroke through anti-oxidant properties. A more recent study corroborates this evidence and further suggests that activation of endocannabinoid receptors - type 2 decreases the damage done to the brain after a stroke due to its activation of microglia and macrophages, proteins which are involved in healing the brain after injury.
So, the literature is mixed and the jury is still out on whether marijuana is good or bad for neurological insults such as stroke. From a close examination of the science, it seems that marijuana use can lead to stroke, however, it can decrease the amount of damage caused by such a stroke. This seemingly paradoxical picture of marijuana on cardiovascular health needs intensive scrutiny from both the clinical and nonclinical researchers in order to produce reliable information for health professionals.
Sources: Journal of Stroke and Cerebrovascular Diseases, Annals of Vascular Surgery, Molecular Brain, Cannabis and Cannabinoid Research, Proceedings of the National Academy of Sciences, Stroke