In 804 adolescents (441 females and 363 males) investigators of the Department of Psychiatry and Psychotherapy of the Charité Hospital in Berlin, Germany, did not find any negative effect on cognitive abilities by cannabis use. Participants were investigated at the age of 14 and 5 years later at the age of 19.
They concluded from their data that “decision making is not impaired when cannabis is used in moderation, and onset of use occurs after the age of 15.” They further wrote that “cross-sectionally, we detected no significant neurocognitive differences before initiation of drug use. However, after controlling for confounders, light cannabis use as well as late-onset thereof was associated with increased decision-making skills both cross-sectionally at follow-up as well as longitudinally compared to non-using controls. (…) We find no evidence to support the presumption that cannabis consumption leads to a decline in neurocognitive ability.”
https://www.sciencedirect.com/science/article/abs/pii/S0885201421000678?via%3Dihub
