Cumulative marijuana use is associated with poorer cognition, or brain functioning, in men with schizophrenia while they are still dependent on the drug, according to a new study.
However, researchers did not find an association between cumulative marijuana use and cognition in schizophrenia patients who used to be dependent on the drug but are not any longer (in remission for at least 6 months).
The study results show that “the state dependent negative effects of cannabis may be reversed with sustained abstinence” in people with schizophrenia, said researchers.
To investigate the effects of marijuana use on cognition in schizophrenia patients, the team recruited 47 male outpatients with the disorder, 18 of whom were currently dependent on the drug.
Of the 29 patients who were not current users, 21 had been formerly dependent on the drug and eight had never been dependent.
The study participants completed a comprehensive set of psychological tests designed to measure cognition. Specifically, the researchers measured the participants’ memory, sustained attention, concentration, psychomotor speed, response inhibition, processing speed, impulsivity and executive function (the ability to solve problems).
Analysis revealed that patients who had used marijuana at any time in their lives had better processing speed than those with no dependence, but there were no significant group differences in other areas of cognition.
The results also revealed a “robust” negative association between cumulative marijuana exposure and cognition across various domains in patients who were currently dependent.
No such associations were found in participants who were not currently dependent on marijuana.
“The present study suggests modest and selective effects of lifetime cannabis dependence on cognitive performance in patients with schizophrenia,” said Rachel Rabin, a doctoral candidate at the University of Toronto.
“While lifetime cannabis users may represent a better functioning subgroup of patients with schizophrenia, cannabis does disrupt cognitive function in that increasing years of cannabis use are associated with worse cognitive performance,” said the researchers.
“Given the high prevalence of cannabis misuse combined with the persistence and significance of cognitive deficits in schizophrenia, large-scale longitudinal investigations determining the true effects of cannabis on cognition are necessary.”
The study is published in the journal, Psychiatry Research.
Source: Psychiatry Research