Marijuana sends blood rushing to brain
Marijuana users have faster blood flow in their brains, even after a month of not smoking, US researchers report.
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.
Dr Ronald Herning and Dr 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 give up marijuana for the four weeks.
The smokers had faster blood flow, both at the start and after a month of abstinence.
They 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," says Herning.
"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."
The researchers 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, say the researchers.
Researchers at Canada's McGill University have reported that chronic consumers of marijuana 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.