Baltimore, MD (04/05/2005)- Regular marijuana use causes changes
in blood flow to the brain that can persist for at least a month after stopping
use
of the drug. The alteration in blood flow could be part of the reason frequent
marijuana users have trouble with memory and decision-making, according to
researchers from the National Institute on Drug Abuse (NIDA).
In a study recently published in the journal Neurology,
researchers measured blood flow to the brain using transcranial Doppler
(TCD) sonography
-- a
technology using ultrasound that measures the velocity of blood flow in vessels.
The device is commonly used to measure blood flow to the brain in patients
with stroke, hypertension, head trauma and other conditions.
The study was done on 54 regular marijuana users, plus 18 non-user volunteers
who were used as controls. The marijuana users were divided into three groups,
depending on the number of joints they smoked per week. There
were a total of 11 light users who smoked an average of 3.5
joints
per week;
23 moderate
users who averaged 16.4 joints weekly, and 20 heavy users who averaged 23
per week. People who were using other types of drugs, had alcohol dependency,
hypertension, major psychiatric disorders or head injury, were not allowed
in the study.
Blood flow was measured and recorded when the subjects entered the study.
Marijuana users then stopped using the drug for a month and were retested.
Blood flow velocity was measured in both the right and left middle cerebral
artery (MCA), and in the right and left anterior cerebral artery (ACA). These
are the main vessels carrying blood and oxygen in the brain. The MCA takes
blood to the frontal and parietal lobes, and the ACA takes blood to the inner
side of the frontal lobe.
"The frontal lobe is involved in lots of different neuropsychological functions.
Executive function is there, some memory, and it's involved in making decisions.
There have been studies that found that people who have used marijuana for
a long time, or a lot of marijuana, tend to have difficulty with the executive
functions," said Jean Lud Cadet, MD, chief of molecular neuropsychiatry at
NIDA, and senior author of the study.
Researchers found that there was increased resistance to blood flow in the
marijuana users compared to the non-users. Increased resistance is not a
good thing and can mean there is less blood reaching smaller vessels in the
brain. It is usually seen in patients with vascular problems such
as hypertension, stroke, diabetes or small vessel diseases in the brain.
Increased resistance may be due to vessels becoming tighter either from
contractions (arteries are lined with muscle tissue) or partial blockage.
Either way, blood is pushed through faster. Dr. Cadet likens it to what happens
when a garden hose is squeezed and water squirts through.
Interestingly, the amount of increased blood flow resistance in marijuana
users in this study was similar to that seen in older adults with cognitive
problems, and was also similar to the amount seen in cocaine users in an
earlier NIDA story, Dr. Cadet said. "The one thing that's sure is that in
older people who have cognitive abnormalities, they also have this kind of
finding," he told Access Excellence.
He cautions that it is not known exactly what the changes in blood flow
of the brains of marijuana users means medically. Neuro-psychiatric tests
were also done on the study subjects, but the findings have not
yet been correlated to the data pertaining to blood flow.
"We'll be able to tell you in the future if there is a correlation between
these changes and the neuro-psychological abnormalities," he said. However,
he added, "If there is resistance in these patients, who are pretty young,
that tells you there might be some abnormalities in the bed of their small
vessels."
Another finding was that blood flow in the brains of mild marijuana uesrs
returned to normal after a one month abstinence, but not in the moderate
or
heavy
users.
This doesn't mean that blood flow would continue to be abnormal in
the heavier users over time. The study lasted only for a month, so it's possible
there
could be changes with longer abstinence, Dr. Cadet said.
end
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