Long

Long-Term Pot Use Takes Toll on Brain

Avid smokers score lower on memory, mental function tests

By Adam Marcus
HealthScoutNews Reporter

TUESDAY, March 5 (HealthScoutNews) -- Many marijuana users say they smoke pot to help them "take the edge off," so it's no surprise the drug makes the mind a bit hazy.

However, smokers who have toked for a long time may cause themselves irreversible brain damage that leads to permanent memory and thinking problems. So says a new study by international researchers who have found the cognitive deficits associated with marijuana use are worse in people with a longer history of taking the drug.

However, at least one cannabis researcher says the findings don't jibe with a recent study showing that even long-term marijuana use causes no appreciable mental deficits.

A report on the findings appears in tomorrow's issue of the Journal of the American Medical Association.

More than 7 million Americans say they smoke marijuana at least once a week. Scientists generally agree that pot dulls the mind for about 12 to 24 hours, and users will suffer on cognitive tests until the drug washes out of their system. However, there's less agreement about whether long-term use of marijuana exacerbates these effects.

The latest study, led by Nadia Solowij, a researcher at the University of New South Wales in Sydney, Australia, suggests the answer may be yes.

Solowij and her colleagues, including scientists in the United States, studied 102 heavy pot smokers seeking treatment for their drug use.

The volunteers, mostly young and middle-aged men, took a battery of nine memory, learning and cognition tests. Half reported taking the drug daily or nearly every day for an average of about 24 years. The rest said they had been smoking just as much, but for roughly half as long -- 10 years, on average.

The tests included word recall tasks, card sorting, time-lapse estimation, and other standardized exams. All were performed after the subjects had refrained from using marijuana for an average of 17 hours.

Long-term users scored worse than short-term users and a control group of 33 non-users on tests measuring recall and attention span, the researchers say. They were able to remember fewer words, retained less and had trouble retrieving information.

Short-term smokers generally scored as well as the non-users, although both groups of users had problems noting the passage of time.

The deficits were in the "moderate to large range," with the biggest difference in word memorization and recall, says Robert Stephens, a psychologist at Virginia Polytechnic Institute and State University and a co-author of the study. "But it's difficult to translate that into daily functioning."

Stephens says those sorts of declines might spell trouble for academic learning or performing a complex task, although there's no evidence of that yet.

Joseph E. Manno, a cannabis expert at Louisiana State University in Shreveport, says the new findings are "consistent with what you would expect from a drug that is cumulative." The question, Manno adds, is how significant the deficits become.

"Are you really, really dangerous, or are you so sedated that you would never engage in any kind of activity that requires skill?" he asks.

However, Dr. Harrison Pope Jr., a Harvard University psychiatrist, says that while the study may be smoke, it's not necessarily fire.

It conflicts with a recent analysis he conducted of a group of studies showing that long-term pot smoking made no appreciable dent in seven of eight standard measures of brain function, and had only a minor impact on one learning test.

In addition, nearly half of the long-term users in the latest study had also regularly used, been dependent on, or been treated for addiction to alcohol or other drugs, which might have affected their memory and cognitive ability.

What's more, says Pope, the pot smokers were all seeking treatment for their habit, while the non-using volunteers were drawn from the community by advertisements. People in treatment programs often have other psychiatric problems, such as anxiety or depression -- and may be taking medication for those conditions -- that can affect their results on cognitive tests. Stephens says his group tried to control for these and other factors, including medication and substance intake.

Thus, Pope says, "we cannot say for sure whether the greater deficits in the long-term users are necessarily attributable to their long-term use." In fact, he adds, his own work implies they might not be. One study he helped conduct showed the impact of marijuana on the brain dissolved when smokers had been off the drug for 28 days.

"As long as there are substantial amounts of the drug still present, there's no question that impairment exists," Pope says. The active ingredient in pot, THC, hangs around in fat, slowly percolating out of the body and causing memory and cognitive hiccups that can linger for days.

"But as to whether it permanently harms the brain, I would say that the jury is still out on that," he says.

What To Do: To learn more about the health effects of marijuana, try the National Institute on Drug Abuse or the Canadian Center on Substance Abuse.

SOURCES: Interviews with Robert Stephens, Ph.D., associate professor, psychology, Virginia Polytechnic Institute and State University, Blacksburg, Va.; Harrison Pope Jr., M.D., biological psychiatry laboratory, McLean Hospital, Harvard Medical School, Belmont, Mass.; Joseph E. Manno, Ph.D., professor, department of emergency medicine, chief, section of clinical toxicology, Louisiana State University Health Science Center, Shreveport, La.; March 6, 2002, Journal of the American Medical Association

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