HAZY VIEW ON HEAVY MARIJUANA USAGE

Heavy, chronic marijuana users suffer memory loss and attention problems
that can affect their work, learning and life, researchers have reported.

But in an indication of the controversy surrounding a drug said to be used
at least weekly by seven million people in the United States, a medical
expert, not involved in the study, questioned the findings and whether the
alleged adverse impact of the drug persists.

The study was published in the Journal of the American Medical Association.

It was based on patients seeking help for marijuana dependence at clinics
in Seattle, Farmington, Connecticut, and Miami, between 1997 and 2000.

The study examined 51 people who had been using marijuana regularly for an
average of 24 years, 51 short-term users and 33 non-users, included as
controls for comparison purposes in the research.

"Long-term users ... performed significantly less well on tests of memory
and attention than non-user controls and shorter-term users with a mean of
10 years' use," the study said.

On one verbal learning test "long-term users recalled significantly fewer
words than either shorter-term users or controls; there was no difference
between shorter-term users and controls.

"Long-term users showed impaired learning, retention and retrieval compared
with controls," the study said.

The authors of the study, Nadia Solowij of the University of New South
Wales in Sydney and colleagues from the Marijuana Treatment Project
Research Group, said their study confirmed and extended previous findings
of cognitive impairments among chronic heavy marijuana users.

"For habitual users, the kinds of impairments observed in this study have
the potential to impact academic achievements, occupational proficiency,
interpersonal relationships and daily functioning," the study said.

But in an editorial in the same issue, Harrison Pope of Harvard Medical
School said "a recent meta-analysis of neuropsychological studies of
long-term marijuana users found no significant evidence for deficits in
seven of eight ... ability areas and only a small effect size for the
remaining area of learning".

Mr Pope said the study did not explore whether the heavy users might have
been taking other drugs that might have accounted for the deficits, or
whether they might have been suffering from anxiety or depression that
could cause the problems.

"Another recent study from our laboratory ... found virtually no
significant differences between 108 heavy cannabis users and 72 controls -
screened to exclude those with psychiatric disorders, medication use, or
any history of significant use of other drugs or alcohol - on a battery of
10 neuropsychological tests after 28 days of supervised abstinence."

Mr Pope, who directs the Biological Psychiatry Laboratory at McLean
Hospital in Massachusetts, said: " At this point the jury is still out on
the question of whether long-term marijuana use causes lasting impairment
in brain function."