Source: Stephen Adams, "Cannabis smoking 'permanently lowers IQ'," The Telegraph, 27 July 2012.
Source: Madeline Meier, et al, "Persistent cannabis users show neuropsychological decline from childhood to midlife," Proceedings of the National Academy of Sciences (PNAS), 30 July 2012.
"Researchers found persistent users of the drug, [marijuana], who started smoking it at school, had lower IQ scores as adults. They were also significantly more likely to have attention and memory problems in later life, than their peers who abstained. Furthermore, those who started as teenagers and used it heavily, but quit as adults, did not regain their full mental powers ..." [Adams]
"Persistent cannabis use was associated with neuropsychological decline broadly across domains of functioning, even after controlling for years of education. Informants also reported noticing more cognitive problems for persistent cannabis users. Impairment was concentrated among adolescent-onset cannabis users, with more persistent use associated with greater decline. Further, cessation of cannabis use did not fully restore neuropsychological functioning among adolescent-onset cannabis users. Findings are suggestive of a neurotoxic effect of cannabis on the adolescent brain and highlight the importance of prevention and policy efforts targeting adolescents." [Meier]
"“For example, individuals who started using cannabis in adolescence and used it for years thereafter showed an average eight-point IQ decline. Quitting or reducing cannabis use did not appear to fully restore intellectual functioning among adolescent-onset former persistent cannabis users,” she said. Although eight points did not sound much, it was not trivial, she warned. It meant that an average person dropped far down the intelligence rankings, so that instead of 50 per cent of the population being more intelligent than them, 71 per cent were." [Adams]
"The cognitive abilities of the 10 per cent of people who started in their 20s - who could loosely be classed as college smokers - also suffered while they were still smoking. However, if they gave up at least a year before their IQ test at 38, their intelligence recovered, suggesting their brains were more resilient and bounced back. Prof. Moffitt said adolescent brains appeared "more vulnerable to damage and disruption" from cannabis than those of fully mature adults." [Adams]
This study gives new meaning to Paul's command, "Likewise exhort the young men to be sober-minded" (Titus 2:9). "Sober-minded" translates the Greek word sophroneo. It literally means "safe mind." It refers to someone who is rational, in the sense of being intellectually sound, and in their right mind. It is commonly connected with the idea of physical abstinence, as in the proverb "a sound mind in a sound body." In classical Greek writings, Aristotle wrote, "By abstaining from pleasures we become sober [sophrones]." He also stated, "He who abstains from physical pleasure, and in this very thing takes delight, is sober [sophron]." The Jewish philosopher Philo defined the opposite of sophrosune, as aphrosune -- a person who "inflamed by wine drowns his whole life in ceaseless and unending drunkenness." A person who uses marijuana is not sober-minded.
A long time ago, Moses warned, "and so it may not happen, when he hears the words of this curse, that he blesses himself in his heart, saying, 'I shall have peace, even though I follow the dictates of my heart' - as though the drunkard could be included with the sober" (Deuteronomy 29:19). People who use drugs, such as alcohol, will deceive themselves into thinking that they are fine while doing what they wish. But soberness and drunkness are not compatible. You can't be stoned and be following God.