Study: Marijuana`s Effects on Brain Are Reversible

Intellectual impairment associated with heavy marijuana use is apparently reversible with abstinence, researchers report.

And marijuana withdrawal symptoms in habitual users are similar to those seen with nicotine withdrawal, according to a second report published in the October issue of the Archives of General Psychiatry.

The lead author of the first report, Dr. Harrison G. Pope, Jr. of McLean Hospital in Belmont, Massachusetts, told Reuters Health, "It appears that cognitive impairment from marijuana use is temporary and related to the amount of marijuana that has been recently smoked rather than permanent and related to an entire lifetime consumption."

Pope and colleagues collected data on three groups of marijuana users. One group consisted of 63 users who had smoked marijuana at least 5,000 times in their lives and were daily marijuana users.

In the second group, there were 45 former marijuana users who had smoked marijuana at least 5,000 times but had used it less than 12 times in the past 3 months. The third group was made up of 72 "controls" who had not smoked marijuana more than 50 times.

People in the study abstained from marijuana for 28 days, during which time the researchers gave them tests that assessed general intellectual function, abstract thinking, sustained attention, verbal fluency and the ability to learn and recall verbal and visuospatial data. Tests were given at the beginning of the study and on days 1, 7 and 28.

Heavy marijuana users had significantly lower scores on word recall lists at the beginning of the study and on the day 1 and day 7 tests compared with non-users. However, by day 28 there were no significant differences between the groups in any of the tests, with no significant association between cumulative lifetime marijuana use and test scores, Pope's group found.

"People who are regular heavy marijuana smokers will exhibit some impairment that lasts days, and possibly even a couple of weeks after they stop smoking--that's the bad news. The good news is that if they abstain from marijuana for longer than 4 weeks, then the residual effects seem to disappear," Pope said.

In the second report, Dr. Alan J. Budney from the University of Vermont in Burlington and colleagues studied withdrawal effects in 12 daily marijuana smokers.

"Comparing our results to studies of nicotine withdrawal, it looks like the magnitude of the severity of withdrawal is similar," Budney said in an interview with Reuters Health. "So as people try to quit smoking marijuana, one can expect them to have problems with withdrawal."

The researchers had the study participants smoke marijuana as usual for 5 days, then abstain for 3 days, smoke again for 5 days and abstain for another 3 days.

Craving for marijuana, decreased appetite, sleep difficulty and weight loss were more common in abstaining periods. Aggression, anger, irritability, restlessness and strange dreams were also significantly increased during abstinence, Budney's team found.

"This highlights the issue that when you treat marijuana-dependent folk, they are going to complain about withdrawal--it is real. If you consider tobacco withdrawal real, you should consider marijuana withdrawal real," Budney stressed.

Source: Archives of General Psychiatry 2001;58:909-915, 917-924.

Source: Reuters
Author: Steven Reinberg
Published: October 17, 2001
Copyright: 2001 Reuters Health

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