Cerebrovascular perfusion in marijuana users during a month of monitored abstinence

Abstract

Objective: To determine possible effects of prolonged marijuana use on the cerebrovascular system during a month of monitored abstinence and to assess how the intensity of current use might have influenced cerebrovascular perfusion in these marijuana users. Method: The authors recorded blood flow velocity in the anterior and middle cerebral arteries using transcranial Doppler sonography in three groups of marijuana users who differed in the intensity of recent use (light: n 11; moderate: n 23; and heavy: n 20) and in control subjects (n 18) to assess the nature and duration of any potential abnormalities. Blood flow velocity was recorded within 3 days of admission and 28 to 30 days of monitored abstinence on an inpatient research unit in order to evaluate subacute effects of the drug and any abstinence-generated changes. Results: Pulsatility index, a measure of cerebrovascular resistance, and systolic velocity were significantly increased in the marijuana users vs control subjects. These increases persisted in the heavy marijuana users after a month of monitored abstinence. Conclusions: Chronic marijuana use is associated with increased cerebrovascular resis- tance through changes mediated, in part, in blood vessels or in the brain parenchyma. These findings might provide a partial explanation for the cognitive deficits observed in a similar group of marijuana users. NEUROLOGY 2005;64:488-493 Marijuana is the most commonly used drug among young persons. 1 Prolonged effects of marijuana on the neurovasculature might be responsible, in part, for the reports of cognitive deficits observed in some of these users 2 because the acute administration of marijuana or delta-9-tetrahydrocannbinal (THC) causes increases in cerebral blood flow in marijuana users 3 and because reduced cerebral blood flow is observed in recently abstinent chronic marijuana us- ers. 4 It remains to be determined whether the re- ported changes in cerebral blood flow might persist over an extended period of monitored abstinence, and whether the intensity of current marijuana use might influence the severity or duration of the perfu- sion deficits associated with use of the drug. In order to address these issues further, three groups of marijuana users differing in the current intensity of use were tested with transcranial Dopp- ler (TCD) sonography early and late during a month of monitored abstinence. Their data were contrasted with those of control subjects. In order to delineate possible effects of marijuana on cerebral vessels, we opted for TCD because TCD assessment is noninva- sive, economical, and rapid. 5 Because TCD is a test that is easily available in clinical neurology settings, it allows for easy replication, unlike some of the more expensive imaging techniques.