So Called "Medical Marijuana" is the gateway drug

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Cognitive Deficits in Marijuana Smokers Persist After Use Stops

Research Findings
Vol. 18, No. 5 (December 2003)

By Jill Schlabig Williams, NIDA NOTES Contributing Writer

NIDA-funded scientists have found that cognitive impairments resulting
from
smoking marijuana can last up to at least 28 days after an individual last
smoked the drug. The more a person had smoked prior to abstinence, the
more
profound this impairment, with marijuana smokers with lower IQs faring
worse
than their higher IQ peers, even if the latter had routinely smoked more
of
the drug.

NIDA-funded researchers Dr. Karen Bolla from the Johns Hopkins University
School of Medicine in Baltimore and Dr. Jean Lud Cadet from NIDA's
Intramural Research Program (IRP) admitted marijuana smokers to IRP's
Clinical Inpatient Research Unit on Hopkins' Bayview campus, tested them
to
ensure they abstained from marijuana use throughout their 4-week stay, and
gave them a battery of neurocognitive tests at the end of the study.

Twenty-two individuals participated. Their average age was 22, 86 percent
were male, and all reported consuming fewer than 14 alcoholic drinks a
week.
The researchers estimated that the group had been smoking marijuana for an
average of 4.8 years. Based on participants' reports of their current
levels
of marijuana use, the researchers grouped them as light, medium, or heavy
smokers. "Determining an exposure index--how many joints participants
smoked
per week--and looking at the range of use in the study population
strengthened our ability to make causal inferences," says Dr. Bolla.

Very heavy abusers smoked an average of 94 joints a week and scored worse
than light abusers (average 11 joints per week) on 24 of the 35
neurocognitive tests, even after 28 days of abstinence. The measures on
which the heavy abusers had comparative deficits included verbal and
visual
memory, executive functioning, visual perception, psychomotor speed, and
manual dexterity. On some tests, quantity of marijuana use accounted for
more than half the variance in test scores. "We found a dose-response
relationship," says Dr. Bolla. "The more marijuana people used, the worse
they performed on the tests, especially those for memory."

"We know a lot about the acute effects of marijuana use, but researchers
are
just now beginning to look at the long-term effects," says Dr. Jag Khalsa
of
NIDA's Center on AIDS and Other Medical Consequences of Drug Abuse. "This
study demonstrates that marijuana smoking has chronic, dose-related
effects
on cognitive impairments up to 28 days after last use. But how long do
these
effects persist beyond that point? That's something we have to examine."

"We have shown that marijuana use is associated with persistent
detrimental
cognitive effects," explains Dr. Bolla. "These results are not
attributable
to use of other drugs, because participants were excluded for current or
past history of significant use of other substances, including alcohol.
Marijuana appears to be harmful when smoked in very large quantities."

The study results also suggested that some people are at higher cognitive
risk from smoking marijuana than others. Cognitive performance in
individuals with lower IQ scores decreased as the number of joints smoked
per week increased, while those with higher IQ scores had fewer decrements
even as marijuana use increased. "This finding demonstrates the concept of
cognitive reserve," says Dr. Bolla. "People with higher IQs do better than
those with lower IQs; the fewer cognitive reserves you have, the more
impact
you will see from a slight change in brain function."

The results of this study are consistent with study findings obtained by
Dr.
Harrison Pope, Jr., at Harvard University McLean Hospital in Belmont,
Massachusetts (see "Studies Show Cognitive Impairments Linger in Heavy
Marijuana Users," NIDA NOTES, Vol. 11, No. 3). Dr. Pope and his colleagues
found that memory and learning problems caused by heavy marijuana smoking
lasted for at least a week after use stopped, although the problems
disappeared within a month. "Since marijuana has a half-life of 4 days,
the
neurocognitive effects seen in Dr. Pope's study after 7 days indicate that
marijuana does have residual effects," says Dr. Khalsa. "Study differences
in longer term effects could be explained by differences in the study
population."
"In the Harvard study," Dr. Bolla notes, "participants were older, ranging
from age 30 to 55; had higher IQs; were more affluent; and were more
likely
to be employed. Our inpatient study was conducted in the inner city with a
younger, poorer population that used marijuana more heavily. Plus, Dr.
Pope
measured lifetime episodes of smoking marijuana, not the current number of
joints smoked per week." In Dr. Bolla's study, duration of use was
associated with a decrease in performance on just one neurocognitive test,
which measured participants' ability to copy a complex figure.

Source

Bolla, K.I., et al. Dose-related neurocognitive effects of marijuana use.
Neurology 59(9):1337-1343, 2002.