Memory up in smoke with
long marijuana use
By CHRISTINE DELL'AMORE
UPI Consumer Health Correspondent
WASHINGTON, March 13 (UPI) -- Smoking marijuana long
term could make your memory and other cognitive skills
go -- quite literally -- to pot.
In a new study of long-term users people who smoked
at least one marijuana cigarette a day for 10 years
performed poorly on a range of standardized tests,
including verbal fluency, verbal memory and learning, as
compared to both those who had lit up for shorter
amounts of time or did not use marijuana at all.
"It will help us understand that cannabis is not such
an innocent drug," said lead author Dr. Lambros Messinis,
a neurologist at the University Hospital of Patras in
His research will be published in the March 14 issue
of Neurology, the scientific journal of the American
Academy of Neurology.
Scientists understand the intoxication effects of
cannabis, but the long-term impacts of the drug on the
mind are not as well-documented. This prompted Messinis
to address what he called a "significant absence" of
studies on the subject.
Messinis and colleagues recruited 64 people from a
drug-abuse treatment program in Athens and divided them
into three groups: long-term frequency users, who had
smoked for at least 10 years; short-term frequency
users, who smoked for five to 10 years, and a control
group of people who may have tried marijuana in the
past, but sparingly. Frequent users ingested marijuana
more than 20 times a month. The participants, aged 17 to
49, were tested to ensure they were not using other
drugs at the time of the analysis.
The subjects also refrained from smoking marijuana
for at least 24 hours in order to avoid the effects of
intoxication altering the experiment.
Researchers then administered various cognitive tests
to participants. The most striking deficits among the
long-term users appeared in verbal learning: the
subjects had difficulty in recalling previously learned
words, for instance. Messinis also discovered the
long-term users had trouble with executive functioning,
or the ability to organize and coordinate simple tasks.
So what does marijuana do once it hits the brain?
Messinis said no one knows for sure, and he did not want
to speculate. However, the Web site of the National
Institute on Drug Abuse suggests it's likely marijuana
attaches to receptors in the brain, interfering with
Sections of the brain with the most receptors include
the cerebellum, the cerebral cortex, and limbic system:
all areas responsible for thinking, problem solving,
balance and memory, among others.
Yet some view the results with skepticism.
For instance, the data does not support the
conclusion that heavy long-term use leads to permanent
deficits, which is implied in the research, said Igor
Grant, a professor of psychiatry and director of the
Center for Medicinal Cannabis Research at the University
of California in San Diego.
"It's not a surprise to anybody that people who are
active users have subtle impairments," Grant said.
Grant authored a 2003 paper in the Journal of the
International Neuropsychological Society, which reviewed
many studies on the topic of long-term cannabis use and
concluded that brain effects, if any, are minimal.
"I have no doubt if I did an identical study I would
come out with same numbers. But I would still be
cautious about drawing the conclusion that marijuana is
responsible for those numbers," said Harrison Pope, a
professor of psychiatry at Harvard Medical School.
That's because it's hard to figure out a chain of
causality when doing marijuana studies. For example,
long-term marijuana users are more likely to have spent
high school stoned, and thus might be less likely to
have boosted their vocabularies reading literature. So
asking them to recall words they are not familiar with
in the first place wouldn't necessarily mean the
marijuana has damaged their brain.
"It's always and forever difficult to tease apart the
confounding variables," said Pope, who has conducted
research on marijuana use for more than 10 years.
In most aspects of science, the only way to answer a
question once and for all is to do a randomized,
controlled trial of 100 people or more, Pope said. But
since giving people marijuana in a clinical setting
poses a rather formidable dilemma, Pope said that he and
other psychiatrists must fall back on messy methodology.
But Messinis is up for the task. Next he plans to
explore two questions still up in the air: whether the
deficits in memory and cognition are reversible, and
also whether a heavier dose of marijuana -- not just
duration -- has a different effect on the mind.