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 Researchers interviewed 1,121 adults 22 to 36 years old about any
history of drug use and also tested participants' urine for evidence
of cannabis and other drugs. Then, participants completed
neuropsychological evaluations, which assess things like memory,
attention, processing speed, executive function and motor skills.
A total of 135 people, or 12%, had positive urine screens for
tetrahydrocannabinol (THC), the chemical associated with marijuana's
psychoactive effects, suggesting they had used cannabis within the
past week. People who tested positive for THC scored worse on tests
of so-called episodic memory and of mental processing speed, the
study found. None of the other brain functions showed a difference.
"This has implications for all cannabis users, but especially
medical cannabis users who may be consuming daily or multiple times
daily for symptom management," said James MacKillop, senior author
of the study and a researcher at McMaster University in Hamilton,
Ontario.
"These individuals would likely have THC chronically circulating in
their system and, in turn, cognitive consequences," MacKillop said
by email. "This applies to heavy recreational users who are
consuming daily too of course."
The findings also suggest that people in high-stakes professions
that require split-second decisions like police and air traffic
controllers might be impaired on the job even when they limit
cannabis use to their time off, MacKillop said.
"Some cognitive consequences are present as long as THC is still
detectable in urine," MacKillop said. "Although the effects were
very small, any (reduction) in performance may have significant
consequences in a critical situation."
Cannabis is one of the most commonly used psychoactive drugs in the
world; an estimated 2.5% of the world's population has reported
cannabis use in the past year, the study team notes in the Journal
of Psychiatry and Neuroscience.
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In the study, 482 participants, or 43%, had never used cannabis.
Another 317 people, or 28%, had only tried cannabis up to 10 times,
while 139 people, or 12%, used cannabis between 11 and 100 times.
A total of 109 people, or 9.7%, had current or previous cannabis use
disorder, which includes chronic use of the drug. This condition was
associated with lower fluid intelligence and cognitive functioning.
One limitation of the study is that the differences in
neuropsychological performance associated with cannabis use were
small, even though they were statistically meaningful.
Still, cannabis users might have short-term impairments that aren't
easy to spot but could be dangerous in certain situations, said
Mary-Ann Fitzcharles, a researcher at McGill University, in
Montreal, who wasn't involved in the study. That's because the
deficits aren't verbal; they relate more to visual and spatial
skills.
"Episodic memory and processing speed were assessed by visual tests,
rather than written/verbal assessment," Fitzcharles said by email.
"The impairment is therefore assessed as being in the visuospatial
domain which is not easily perceived to be an impairment by an
individual," Fitzcharles added. "For example, persons may believe
that they are perfectly competent to drive a car, operate a crane,
or respond quickly in an unexpected situation after cannabis use,
but in fact are impaired and at risk."
SOURCE: https://bit.ly/2JPd6gq Journal of Psychiatry and
Neuroscience, online June 27, 2019.
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