Mar 06, 2002
Adding to the controversy about the long-term effects of marijuana use, results of a new neuropsychological study indicate that long-term use is associated with impaired memory and attention, which lasts beyond intoxication and becomes worse with continued use.
Dr. Nadia Solowij, from the University of New South Wales, Sydney, Australia, and colleagues studied 102 near-daily marijuana users undergoing treatment for drug dependence. Among these subjects, 51 had used marijuana for a mean of 23.9 years and 51 had used marijuana for a mean of 10.2 years. The researchers compared these subjects with 33 individuals who had never used marijuana.
The subjects underwent neuropsychological tests, which measured memory, attention, and executive functioning. The tests were given before the subjects began the treatment program after a median of 17 hours of abstinence, according to the report in The Journal of the American Medical Association for March 6.
Compared with short-term marijuana users and controls, subjects who were long-tern marijuana users performed significantly worse on the tests that examined memory and attention.
Long-term marijuana users recalled significantly fewer words on the Rey Auditory Verbal Learning Test compared with short-term marijuana users (p = 0.001) or controls (p = 0.005). There was no difference between controls and short-term marijuana users in these measures, the researchers found.
"Performance measures often correlated significantly with the duration of cannabis use, being worse with increasing years of use, but were unrelated to withdrawal symptoms and persisted after controlling for recent cannabis use and other drug use," Dr. Solowij and colleagues write.
In a related editorial, Dr. Harrison G. Pope, Jr. takes issue with the findings by Solowij et al. Dr. Pope notes that among other problems there were no data available on the cognitive functioning of the subjects before their first marijuana use, that many subjects used alcohol and other drugs, and they were only abstinent for 17 hours.
"Even if lifetime duration of cannabis use is associated with greater impairment after 17 hours of abstinence, the data are insufficient to know whether greater impairment would be present a week or a month later," Dr. Pope adds. "Despite the important contributions of this new study, we must still live with uncertainty."
© 2002 Reuters Ltd