MARIJUANA AFFECTS BLOOD FLOW TO BRAIN

Marijuana users experience changes of blood flow in the brain,
possibly explaining why some have trouble remembering and thinking.
Smokers in a study had a higher resistance to blood flow in the brain,
possibly caused by a narrowing of blood vessels, said Ronald Herning
of the National Institute on Drug Abuse. "This suggests marijuana use
leads to abnormalities in the small blood vessels in the brain."
Pulsatility index level, or resistance to blood flow, of smokers "was
somewhat higher than of people with chronic high blood pressure or
diabetes."

While it improved after a month of not smoking for light to moderate
smokers, it lasted longer for heavy smokers. Light use is defined as
two to 15 joints a week, and heavy use 78 or more.