Dette er favoritten min når det gjelder cannabis-studier:
Current and former marijuana use: preliminary findings of a longitudinal study of effects on IQ in young adults
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).
Altså en godt designet studie som viser en høyere økning i IQ hos brukere enn ikke-brukere. Hos "tunge" brukere var det en nedgang, men som det står i tolkningen:
A negative effect was not observed among subjects who had previously been heavy users but were no longer using the substance.
Med en liten pause kan nok de tunge brukerne finne opp kruttet og spille sjakk igjen.