A study has shown that people who start smoking marijuana as teens can have a decreased, permanent IQ loss as adults. The highly-publicized study followed over 1000 participants for 38 years. Those participating were interviewed at age 18, 21, 26, 32 and 38. In addition, Neuropsychological testing was completed at 13 years of age and again at 38 years of age. The results showed adolescents who smoked marijuana lost an average of 8 IQ points, which is a significant loss. Even those who stopped smoking after their teenage years did not regain their IQ, indicating that the loss was permanent. Interestingly, those in the study who did not smoke marijuana saw no decrease and even a slight increase in IQ from ages 13 to 38. This study was supported by scientists in the United States and around the world.
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