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Frequent Marijuana Use May Affect Brain Function But Not Structure

Date:
April 3, 2000
Source:
University Of Iowa
Summary:
Recent University of Iowa Health Care studies indicate that some people who frequently use marijuana have substantially lower blood flow to certain parts of their brains; however, smoking the illicit drug does not affect brain size or structure.
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IOWA CITY, Iowa -- Recent University of Iowa Health Care studies indicate that some people who frequently use marijuana have substantially lower blood flow to certain parts of their brains; however, smoking the illicit drug does not affect brain size or structure.

"Although marijuana is the most widely used illicit drug, surprisingly little attention has been given to the impact of frequent marijuana use on the structure or functioning of the human brain," said Robert I. Block, Ph.D., UI associate professor of anesthesia and lead investigator for the studies. "We wanted to examine these questions."

The UI findings appear in separate articles in two recent issues of NeuroReport.

"The question of whether marijuana use produces harmful effects is important because marijuana is the most popular illegal drug, and also because there is a lot of interest in its potential value as a medicine," Block said. "Many people believe that harmful effects have not been proven as clearly with marijuana as with most other illegal drugs. Our research showed some fairly dramatic changes in brain blood flow in some frequent marijuana users, even after the immediate effects of smoking had worn off."

In one study, Block and his colleagues used positron emission tomography (PET) scanning techniques to determine whether frequent marijuana use affected brain function. They compared regional cerebral blood flow in 17 current, frequent young adult marijuana users with 12 comparable, control subjects who did not use marijuana. During the study, the subjects were lying quietly and did not perform any test and were not given any specific directions about what to think about. The marijuana users, who were using marijuana seven or more times weekly on average, were required to abstain from using the drug for at least 26 hours prior to the scan to eliminate short-term effects of marijuana smoking.

The scan results showed that the marijuana users had up to 18 percent lower blood flow than controls in a large region--over a cubic inch of brain tissue--at the back of the brain, in the posterior cerebellum. There was very little effect of marijuana use anywhere else in the brain. Changes in brain blood flow usually correspond to changes in brain activity, so diminished blood flow indicates altered brain function in some frequent marijuana users.

"The idea that frequent marijuana use impairs mental abilities is still controversial, but several recent studies, including our own, support such an association," Block said. "Although the cerebellum was traditionally thought mainly to be involved in controlling movements, more recent evidence has shown that it also plays a role in memory, attention, and other mental abilities. Some cognitive effects of marijuana use may be related to this lower activity of the posterior cerebellum."

Block said that in past studies he and his colleagues have found changes in blood flow in several parts of the brain, including but not limited to the cerebellum, when frequent marijuana users perform memory and attention tests.

"The most impo


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Materials provided by University Of Iowa. Note: Content may be edited for style and length.


Cite This Page:

University Of Iowa. "Frequent Marijuana Use May Affect Brain Function But Not Structure." ScienceDaily. ScienceDaily, 3 April 2000. <www.sciencedaily.com/releases/2000/03/000331090541.htm>.
University Of Iowa. (2000, April 3). Frequent Marijuana Use May Affect Brain Function But Not Structure. ScienceDaily. Retrieved June 20, 2024 from www.sciencedaily.com/releases/2000/03/000331090541.htm
University Of Iowa. "Frequent Marijuana Use May Affect Brain Function But Not Structure." ScienceDaily. www.sciencedaily.com/releases/2000/03/000331090541.htm (accessed June 20, 2024).

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