A carefully done peer-reviewed study has demonstrated unequivocally that pot smoking in teenagers can result in a significant decline in IQ that appears to be permanent. The neurotoxic effect of cannabis on the adolescent brain highlights the importance of prevention and policy efforts targeting adolescents. The authors of this study say "Prevention and policy efforts should focus on delivering to the public the message that cannabis use during adolescence can have harmful effects on neuropsychological functioning, delaying the onset of cannabis use at least until adulthood, and encouraging cessation of cannabis use particularly for those who began using cannabis in adolescence."
Their findings suggest that regular cannabis use before age 18 years of age predicts impairment. In the study, the most persistent adolescent-onset cannabis users evidenced an average 8-point IQ decline from childhood to adulthood. Cannabis use in adolescence causes brain changes that result in neuropsychological impairment. "Several lines of evidence support this possibility (24⇓⇓⇓⇓⇓⇓–31, 33, 34). First, puberty is a period of critical brain development, characterized by neuronal maturation and rearrangement processes (e.g., myelination, synaptic pruning, dendritic plasticity) and the maturation of neurotransmitter systems (e.g., the endogenous cannabinoid system), making the pubertal brain vulnerable to toxic insult (33). Second, cannabis administration in animals is associated with structural and functional brain differences, particularly in hippocampal regions, with structural differences dependent on age and duration of exposure to cannabinoids (33). Third, studies of human adolescents have shown structural and functional brain differences associated with cannabis use (26, 29, 35). The association between persistent cannabis use and neuropsychological decline was still apparent after controlling for years of education. However, the toxic effects of cannabis on the brain may result in impaired neuropsychological functioning, poor academic performance, and subsequent school dropout, which then results in further neuropsychological decline.
"Our finding of neuropsychological difficulties among adolescent-onset former persistent cannabis users who quit or reduced their use for 1 year or more suggests that neuropsychological functioning is not fully restored in this time.
"Increasing efforts should be directed toward delaying the onset of cannabis use by young people, particularly given the recent trend of younger ages of cannabis-use initiation in the United States and evidence that fewer adolescents believe that cannabis use is associated with serious health risk (42). Quitting, however, may have beneficial effects, preventing additional impairment for adolescent-onset users."
Madeline H. Meier, Avshalom Caspi, Antony Ambler, HonaLee Harrington, Renate Houts, Richard S. E. Keefe, Kay McDonald, Aimee Ward, Richie Poulton, and Terrie E. Moffitt
Persistent cannabis users show neuropsychological decline from childhood to midlife
PNAS 2012 109 (40) E2657–E2664; published ahead of print August 27, 2012.
Just saying . . .