A recent study of adult twins suggest cannabis use at any age has little to no effect on intelligence. The study, conducted by the National Academy of Sciences of the United States of America used a "quasi experimental" process to filter through data and identify contributing factors of their findings. One twin used cannabis over an extended period of time while the other twin didn't. In the end, the study was able to conclude cannabis does not have a negative effect on one's intelligence, including the intelligence associated with I.Q. scores.
The study states that, "Among pairs of twin discordant for marijuana use, we assessed intelligence quotient (IQ) score changes while adjusting for the effects of genetic influences and other factors shared by members of the same twin pair. Results suggest that familial confounds underlie the association between adolescent marijuana use and declining IQ scores"
After taking into consideration a plethora of factors, the study concluded that, "Evidence from these two samples suggests that observed declines in measured IQ may not be a direct result of marijuana exposure but rather attributable to familial factors that underlie both marijuana initiation and low intellectual attainment."
The study comes at a pivotal time in U.S. history when public support for cannabis legalization is at an all-time high. Opponents to legalization have made numerous claims through the years that cannabis use, particularly at a young age, has a significant negative impact on one's intelligence.
Despite making these erroneous claims, prohibitionists have not been able to produce proof that cannabis use is detrimental to a young person's intelligence. The closest prohibitionists have come to backing claims have been statistical anomalies that are neither consistent nor replicated.
Pro-cannabis health professionals have long suspected cannabis had no negative impact on intelligence. What better way to confirm the theory than to find sets of twins who make the study twice as useful.