STUDY: POT DOESN'T CAUSE PERMANENT BRAIN DAMAGE

LOS ANGELES (Reuters) - Smoking marijuana will certainly affect
perception, but it does not cause permanent brain damage, researchers
from the University of California at San Diego said on Friday in a
study.

"The findings were kind of a surprise. One might have expected to see
more impairment of higher mental function," said Dr. Igor Grant, a
UCSD professor of psychiatry and the study's lead author. Other
illegal drugs, or even alcohol, can cause brain damage.

His team analyzed data from 15 previously published, controlled
studies into the impact of long-term, recreational cannabis use on the
neurocognitive ability of adults.

The studies tested the mental functions of routine pot smokers, but
not while they were actually high, Grant said.

The results, published in the July issue of the Journal of the
International Neuropsychological Society, show that marijuana has only
a marginally harmful long-term effect on learning and memory.

No effect at all was seen on other functions, including reaction time,
attention, language, reasoning ability, and perceptual and motor
skills. Grant said the findings are particularly significant amid
questions about marijuana's long-term toxicity now that several states
are considering whether to make it available as a medicinal drug.

In California, growing marijuana for medical purposes is legal under a
voter-approved law.

The UCSD analysis of studies involving 704 long-term cannabis users
and 484 nonusers was sponsored by a state-supported program that
oversees research into the use of cannabis to treat certain diseases.

Anecdotal evidence has shown that marijuana can help ease pain in
patients with diseases like multiple sclerosis or prevent severe
nausea in cancer patients, but the effects have yet to be proven in
controlled studies, Grant said.

The UCSD research team said the problems observed in learning and
forgetting suggest that long-term marijuana use results in selective
memory defects, but said the impact was of a very small magnitude.

"If we barely find this tiny effect in long-term heavy users of
cannabis, then we are unlikely to see deleterious side effects in
individuals who receive cannabis for a short time in a medical
setting," Grant said.

In addition, he noted that heavy marijuana users often abuse other
drugs, such as alcohol and amphetamines, which also might have
long-term neurological effects.

Some of the research studies used in the analysis were limited by the
numbers of subjects or insufficient information about factors like
exposure to other drugs or whether participants suffered from
conditions like depression or personality disorders.

"If it turned out that new studies find that cannabis is helpful in
treating some medical conditions, this enables us to see a marginal
level of safety," Grant said.