LONG-TERM MARIJUANA USE MAY FOG THE BRAIN

Long-term users of marijuana gradually become worse at learning and
remembering things, a new study suggests.

=93It definitely fogs your brain,=94 says Lambros Messinis, who led the
study at the University Hospital of Patras in Greece.

Messinis and colleagues tested the mental abilities of 20 long-term
users who had taken marijuana heavily =AD smoking at least four joints a
week =AD for an average of 15 years. Their brains were rustier than
those of 20 short-term users =AD who had averaged seven years of use =AD
and 24 controls who had used the drug sporadically or not at all.

Long-term users performed worse in tests to measure memory, learning
ability and the capacity to recall information. Asked to recall lists
of 15 words that they had seen earlier, for example, the long-term
users averaged seven, compared with nine recalled by short-term users
and 12 by controls.

=93Long-term users found it very difficult to learn through new
information given verbally,=94 says Messinis. =93It's not to do with lack
of attention but more the encoding process of memory.=94 Separate tests
to probe attention span found that long-term users were able to pick
up information immediately, without trouble.

Initial ability

Although the study is retrospective =AD that is, the subjects were not
tested on their cognitive abilities before they took up marijuana =AD
the researchers are confident that the long-term users' abilities were
not significantly different from the other groups from the beginning.
They used a standard test to estimate the long-term users' original
intellectual abilities.

Messinis gave subjects the tests at least 24 hours after they had last
taken the drug, to make sure they were not still under the influence.
=93It wasn't while they were high,=94 he says.

=93Importantly, we don't know if it=92s reversible,=94 he says. To find
out,
he and his colleague plan to re-test the same subjects after
abstinence periods of at least a month.

Nadia Solowij, at the University of Wollongong in Australia, says the
new findings back previous work by her and colleagues, published in
the Journal of the American Medical Association in 2002.

=93The authors appear to have used the same rigorous criteria for
inclusion in their study and confirm that the duration of cannabis use
progressively impacts upon cognitive functions,=94 she told New Scientist.

Journal reference: Neurology (vol 66, p 737)