CANNABIS USE 'DULLS THE BRAIN'

The Study Tested 102 Heavy Users Of The Drug

Long term marijuana users may have worse memories and poorer attention
spans than other users of the drug, scientists say.

Memory and attention span got "significantly" worse the longer a user had
been taking the drug, according to tests done on those entering a US drugs
treatment programme.

But it is not clear whether giving up the drug will enable users to
recover, and the research fuels the scientific debate over the true impact
of marijuana use on the brain.

The research - published in The Journal of the American Medical Association
(Jama) - shows habitual users may suffer academically, at work and in their
interpersonal relationships, its authors say.

Impaired Learning

The study analysed near daily cannabis users; 51 long-term users, 51
shorter-term users, and 33 non-users.

The tests to assess attention, memory, and other brain functions were done
after an average abstinence of 17 hours.

There were clear differences between those who had used the drug for 24
years, and those who had taken it for a decade.

In verbal learning tests, long-term users recalled fewer words than
shorter-term users or controls.

Long-term users showed impaired learning, retention, and retrieval compared
with controls and both user groups performed poorly on a time estimation task.

The authors said performance "correlated significantly with the duration of
cannabis use, being worse with increasing years of use".

Can Brain Recover?

The research team was led by Nadia Solowij, of the University of New South
Wales, Australia, with colleagues with the Marijuana Treatment Project
Research Group - and the study was done in the US between 1997 and 2000.

But Dr Harrison Pope, of the Biological Psychiatry Laboratory, at McLean
Hospital, Harvard Medical School, said other recent studies had shown only
limited "cognitive" impairment among long term users.

"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," he
writes in the same issue of Jama.