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Long-Time Pot Users Show
Mental Deficits
Tue Mar 5, 5:37 PM
ET
By Amy Norton
NEW YORK (Reuters
Health) - Long-time, heavy marijuana users may eventually see their
memory and attention span go up in smoke, new research suggests.
Investigators found
that, among pot smokers seeking treatment for marijuana dependence,
long-time users performed more poorly on tests of memory and
attention than shorter-term users and non-users.
The findings show
that over time, marijuana smoking can cause intellectual impairments
that "endure beyond the period of intoxication" and worsen the
longer a person uses the drug, the study authors report in the March
6th issue of The Journal of the American Medical Association.
But another
researcher not involved in the study pointed to shortcomings in the
work that he says make it tough to draw that conclusion.
In an accompanying
editorial, Dr. Harrison G. Pope, Jr. notes that marijuana users who
seek drug treatment do not necessarily reflect users in general,
since these individuals may have other health issues such as anxiety
or depression.
In the study,
researchers led by Dr. Nadia Solowij of the University of New South
Wales in Sydney, Australia studied 102 pot-smoking Americans and 33
non-users. Marijuana users typically smoked every day, with
long-time users doing so for an average of 24 years. Shorter-term
users had smoked for about 10 years, on average. The vast majority
said that they currently were not using other drugs, or did so only
occasionally.
Results of the
mental functioning tests--taken after at least 12 hours of
abstinence--showed that long-time users performed less well than
shorter-term users and non-users.
"We found that
long-term users had problems with learning, storage of learned
information and retrieval of information from memory," Solowij told
Reuters Health.
This does not mean
the drug caused brain damage in these cases, she said, explaining
that the impairments seen in long-time users were "relatively
subtle."
Still, Solowij
noted, the deficits could affect daily functioning--hindering, for
example, a person's ability to study or remember an item he or she
just read.
But although such
deficits, if prolonged or irreversible, would be of "grave concern,"
other studies have found no such impairments in long-time marijuana
users, according to Pope, a researcher at Harvard Medical School and
McLean Hospital in Belmont, Massachusetts.
Pope and his
colleagues recently found "virtually no significant differences"
between heavy marijuana users and non-users on a battery of
neuropsychological tests.
Part of the
difficulty in sizing up the impact of marijuana is weeding the
drug's effects out from the "background noise" of other factors,
like psychiatric problems and abuse of other drugs, according to
Pope. In this study, nearly half of the long-time marijuana users
had in the past regularly used or abused alcohol or other drugs.
But there are also
plausible biological reasons for why sustained marijuana use could
affect things like memory. Solowij noted that the brain receptors
the drug acts on exist in large numbers in regions involved in
memory. Over the years, she said, marijuana exposure might change
the way these receptors and other brain chemicals operate.
According to Pope,
it seems almost certain that marijuana produces short-lasting mental
deficits, but whether they endure or worsen over time is still
unclear.
Also unknown is
whether any impairments are reversed after a person stops smoking
pot, Solowij pointed out.
"We do not yet know
whether the impairments recover after stopping or reducing
(marijuana) use," she said. "We are currently investigating this
question."
SOURCE: The Journal
of the American Medical Association 2002;287:1123-
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