Bill Clinton might as well have inhaled: New Canadian research suggests
marijuana does not have lasting effects on a person's intelligence.

A preliminary study conducted by Carleton University researchers found
heavy marijuana use -- defined as smoking five or more joints a week --
drives down a person's intelligence quotient (IQ) by an average of 4.1 points.

The effect, however, appears to be temporary: Teens who had smoked
marijuana heavily but had quit for at least three months seemed to rebound
to their former levels of intelligence, challenging the notion that the
drug permanently damages one's brain.

"We conclude that marijuana does not have a long-term negative impact on
global intelligence," the researchers note in their the study, which
appears in the Canadian Medical Association Journal today.

"This lack of a negative impact among former heavy users is striking."

The findings will likely be used by advocates of decriminalization as
further proof that marijuana is harmless and should be legalized, said Dr.
Peter Fried, the lead author. The research, however, has limitations that
must be acknowledged, he warned.

"Marijuana produces a high, which is nice, no objective person will ever
dispute that," he said. "But to pretend that that's the only effect is just
not realistic or factual."

The most common reason the study participants stopped smoking marijuana,
for example, was because they felt it affected their short-term memory.

Dr. Fried, a professor of psychology at Carleton, was in an advantageous
position to study the long-term effects of marijuana use because he has
been tracking the health of 160 teenagers since they were born in the late
1970s. The original intent of his project was to study the effects of
prenatal exposure to marijuana or cigarettes.

For this study, Dr. Fried and his colleagues were able to compare the IQ
scores of 70 participants when they were nine to 12 years of age, before
they were exposed to marijuana, with their scores at ages 17 to 20.

An IQ score, however, is only a general measure of intelligence. It does
not account for specific cognitive functions, such as memory loss and
attention levels, Dr. Fried noted.

And the participants are still young, so using the drug could affect them
in the future in ways that have not yet surfaced, he added.

The participants were asked specific questions about their past marijuana
use and gave urine samples. Of the 70 teenagers who took part, nine were
defined as current light users (they smoked less than five joints a week);
another nine smoked marijuana regularly at one time, but had abstained for
at least three months. Fifteen teens were classified as current heavy users
and another 37 had never regularly used the drug. Most are from
middle-class families in and around Ottawa.

Current marijuana users who smoked more than five joints a week were the
only participants whose IQs were negatively affected.

Dr. Fried plans to double the sample size and conduct a more in-depth
analysis of marijuana's long-term effects on specific brain tasks, such as
processing speed and memory, provided he receives funding for the project.

A controversial Australian study suggested heavy and chronic marijuana
users suffer memory loss and attention problems that can affect their
careers, learning and life. The study, conducted by researchers at the
University of New South Wales, examined 51 people who had been using
marijuana regularly for 24 years and 51 short-term users.

The current study was sponsored by the U.S. National Institute on Drug
Abuse, part of the National Institutes of Health. An estimated 1.5 million
Canadians smoke marijuana for recreational purposes.

Pubdate: Tue, 02 Apr 2002
Source: National Post (Canada)
Copyright: 2002 Southam Inc.
Author: Mary Vallis