Author Affiliation: Biological Psychiatry Laboratory, McLean Hospital, Harvard Medical School, Belmont, Mass.
In this issue of THE JOURNAL, Solowij and colleagues1
report a variety of neuropsychological deficits in long-term cannabis users
who were tested a median of 17 hours after their last reported cannabis intake.
Their findings of impairments in memory and attention are not surprising since
several large and well-controlled studies have found similar deficits on neuropsychological
tests administered to long-term cannabis users after 12 to 72 hours of abstinence.2- 5 If these
deficits are brief and reversible (ie, due to a residue of cannabinoids lingering
in the brain or to withdrawal effects from abruptly stopping the drug), they
might not be a serious threat. However, if these deficits are prolonged or
irreversible (ie, due to neurotoxicity from years of cumulative cannabis exposure),
they become a matter of grave concern. The findings of Solowij and colleagues
favor the latter possibility in that longer-term cannabis users in the study
often showed significantly greater deficits than shorter-term users, and neuropsychological
performance measures were often negatively correlated with lifetime duration
of use. Furthermore, these correlations could not be explained by greater
withdrawal symptoms or heavier recent cannabis consumption among the longer-term
users. Solowij and colleagues1 conclude that
"our results confirm that cognitive impairments develop as a result of prolonged
cannabis use . . . and [that] they worsen with increasing years of use."
Pope, Jr HG. Cannabis, Cognition, and Residual Confounding. JAMA. 2002;287(9):1172–1174. doi:10.1001/jama.287.9.1172