MEDICAL EVIDENCE ON MARIJUANA GOES BOTH WAYS

SACRAMENTO, CALIF. -- Sparked anew by Gov. Arnold Schwarzenegger's
call for the state to study the legalization of marijuana, both sides
in the smoldering pot debate point to research to bolster their positions.

Such recitation of conflicting marijuana studies can be manipulated
and selected buffet-style to serve whatever political and health
agenda is being touted.

Even governmental findings can be contradictory. In 1999, for
instance, the Office of National Drug Control Policy asked the
Institute of Medicine to review evidence. The institute found that,
"except for the harms associated with smoking, the adverse effects of
marijuana use are within the range of effects tolerated for other medications."

Yet in 2006, the Food and Drug Administration ruled that marijuana
has no health benefits and has known and proven harms. It is
classified a Schedule 1 drug -- the highest risk of addiction -- in
the Controlled Substances Act.

Wading through the medical literature, though, makes those
conclusions less cut and dried.

"When I was a resident in Kaiser in San Francisco in 1978, I gave a
lecture to physicians on marijuana, and I remember my conclusion at
that time was that you can find in the literature whatever you were
looking for," says Dr. Donald Abrams, a University of California, San
Francisco, oncologist and leading medical marijuana researcher.
"'Marijuana is good for asthma.' 'Marijuana's bad for asthma.'
'Marijuana causes schizophrenia.' 'Marijuana (decreases)
schizophrenia.' And, you know, the evidence is still like that."

There are many factors, of course. As noted by UCLA pulmonologist
Donald Tashkin, who has studied marijuana's effects on the lungs for
three decades, "That's just the nature of medical science. You have
to deal with variability. The population studied may be different or
the methods used to study may differ."

Yet when the arguments for legalization of marijuana, both for
medicinal and recreational use, are put forth, solid medical science
often gets clouded in an ideological haze.

"Although we like to say we separate politics from science, with
medical marijuana, that's really difficult," Abrams says. "It depends
on who does the study, where it's published and what their agenda is."

Bearing in mind those caveats, here is a look at the research on
marijuana's effect in areas critical to health.

Lungs

UCLA's Tashkin studied heavy marijuana smokers to determine whether
the use led to increased risk of lung cancer and chronic obstructive
pulmonary disease, or COPD. He had hypothesized that there would be a
definitive link between cancer and marijuana smoking, yet the results
proved otherwise.

"What we found instead was no association and even a suggestion of
some protective effect," says Tashkin, whose research was the largest
case-control study ever conducted.

Tobacco smokers in the study had as much as a 21-fold increase in
lung cancer risk. Cigarette smokers, too, developed COPD more often
in the study, and researchers found that marijuana did not impair
lung function.

Tashkin, supported by other research, concluded that the active
ingredient tetrahydrocannabinol has an "anti-tumoral effect" in which
"cells die earlier before they age enough to develop mutations that
might lead to lung cancer."

However, the smoke from marijuana did swell the airways and lead to a
greater risk of chronic bronchitis.

"Early on, when our research appeared as if there would be a negative
impact on lung health, I was opposed to legalization because I
thought it would lead to increased use and that would lead to
increased health effects," Tashkin says.

"But at this point, I'd be in favor of legalization. I wouldn't
encourage anybody to smoke any substances, because of the potential
for harm. But I don't think it should be stigmatized as an illegal substance.

Cognitive Function

A 2006 study in the journal Neurology found that speed of thinking,
attention and verbal fluency were affected by as much as 70 percent
by long-term heavy use (four or more joints per week).

But a 2003 review of literature in the Journal of the International
Neuropsychological Society found that marijuana smoking had a "small
effect" on memory in longtime users.

However, users had no lasting effects in reaction time, attention or
verbal function.

"Surprisingly, we saw very little evidence of deleterious effects,"
Dr. Igor Grant, researcher at the University of California, San
Diego, School of Medicine, said in a statement.

Other studies: A 2002 study in the Journal of the American Medical
Association found that heavy users did worse on recall memory tests.
A 2006 study in Greece showed users had slower mental-processing
speed than the control group.

Then again, a 2007 study at the University of Lausanne in Switzerland
found that students who smoked marijuana had better grades than those
who used only tobacco or those who did not smoke any substance.

In terms of brain development, a 2000 study in the Journal of
Addictive Diseases found changes in brain structure in those who
started using marijuana before age 17 but not in those who started at
an older age.

A 2009 Children's Hospital of Philadelphia study used brain imaging
to show that heavy adolescent users are more likely to have disrupted
brain development in regions involving memory, attention, decision
making and language.

But a 2008 Ohio State University study found that marijuana can
reduce brain inflammation and perhaps reduce memory impairment that
could delay Alzheimer's disease.

Psychosis

Yes, there is an increased risk in psychotic behavior and long-term
risk of mental illness from marijuana use, according to a 2007 review
of literature commissioned by Great Britain's Department of Health
and published in the Lancet.

But the risk is small, because the risk of developing psychosis in
the general population is 3 percent over a lifetime and rises to 5
percent for marijuana users, lead researcher Stanley Zammit told the
Los Angeles Times. "So 95 percent of the people are not going to get
psychotic, even if they smoke on a daily basis," he told the paper.

In 2005, New Zealand researchers studied a group of people with a
gene variant the researchers believe predisposes that group to
developing psychosis. Those in the group who smoked marijuana as
teens had a tenfold increase in risk of psychosis than those who abstained.