[thechat] marijuana and intelligence

Judah McAuley judah at wiredotter.com
Tue Apr 2 12:19:01 CST 2002


deke wrote:
> On 2 Apr 2002 at 10:11, rudy posted a message which said:
>
>
>>but am i reading this correctly?  light use *increases* intelligence? --
>
>
>>   Results: Current marijuana use was significantly correlated
>>   (p < 0.05) in a dose-related fashion with a decline in IQ over
>>   the ages studied. The comparison of the IQ difference scores
>>   showed an average decrease of 4.1 points in current heavy
>>   users (p < 0.05) compared to gains in IQ points for light current
>>   users (5.8), former users (3.5) and non-users (2.6).
>
>
> I'm not sure they have cause and effect right. The level of marijuana
> use is self-selected, rather than being randomly assigned, which makes
> it an entirely different study than the results would indicate.
>
> People of higher intelligence generally have greater curiosity - and
> many of the "drugs of abuse" started out being used first by the
> intelligensia.
>
> However, marijuana gets you *stoned*. You still may be *curious* while
> you are stoned, but you aren't very likely to learn much.
>
> deke

This isn't quite right either.  The values that they report (5.8, 3.5,
and 2.6) are not IQ values, they are IQ *difference* values.  Meaning
that they are how much a groups IQ has changed during the study period.
  Self-selecting doesn't really come into it.  If it were not a
time-related variable that followed the same group, then self-selection
would be a major factor.  But the design is reasonably solid from what I
  read.

That being said, the research also did not say that light current users
got smarter than non-users over the study time period.  The difference
in IQ change was not significantly different when comparing changes
between light current users and non users.  The only significantly
different group is current heavy users.

Bottom line of the study:  Marijuana use is not associated with any
detectable long-term decline in overall intelligence (IQ).  Current
heavy use is associated with a decline in IQ (median change of 4
points).  Mild/moderate usage is not associated with IQ decline.  Using
and then stopping appears to have no long-term effects (3 months or more
of abstinence).

Interesting side notes:  Current heavy users still had above normal IQ
results and would have been considered "fine" if their IQ had not been
compared with their pre-teen, pre-use scores.  None of the potential
confounding variables or cofactors (Family income, education level,
alcohol use, etc) was a predictor of marijuana use.

Well done study.  Thanks for passing it along Rudy.

Judah





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