POT ALTERS BLOOD FLOW: STUDY

Narrows Arteries

Affects Memory

WASHINGTON-- (reuters) Marijuana users have faster blood flow in their
brains, even after a month of not smoking, U.S. researchers reported Monday.

The findings suggest they have narrowed arteries, similar to patients with
high blood pressure and dementia, and could help explain reports that heavy
marijuana users have trouble on memory tests, says the researchers at the
National Institute on Drug Abuse in Baltimore.

Ronald Herning and Jean Lud Cadet tested 54 marijuana users, who smoked
anywhere between two and 350 joints a week, and 18 non-smokers.

They used Doppler sonograms to measure blood flow in volunteers' brains at
the beginning of the study and a month later, after everyone agreed to
abstain from marijuana for the four weeks.

The smokers had faster blood flow, both at the start and after a month of
abstinence, Herning and Cadet reported in the journal Neurology.

The smokers also had a higher pulsatility index score, or PI, which
measures the amount of resistance to blood flow. The researchers believe
the higher PI is caused by narrower blood vessels.

"The marijuana users had PI values that were somewhat higher than those of
people with chronic high blood pressure and diabetes," Herning says in a
statement.

"However, their values were lower than those of people with dementia. This
suggests that marijuana use leads to abnormalities in the small blood
vessels in the brain."

They found that blood flow improved in people who smoked up to 70 marijuana
cigarettes a week -- people they defined as moderate users -- after a month
of avoiding cannabis.

Heavy users, who smoked up to 350 joints a week, saw no change in blood
flow even after a month, the researchers says.

Researchers at Montreal's McGill University have reported that chronic
consumers of cannabis lose molecules called CB1 receptors in the brain's
arteries. This reduces blood flow to the brain, causing attention deficits,
memory loss, and impaired learning ability.