Depending on when your stoner friends got started, they may or may not be self-reporting accurately. From the same link : > Our findings suggest that regular c

Depending on when your stoner friends got started, they may or may not be self-reporting accurately. From the same link : > Our findings suggest that regular cannabis use before age 18 y predicts impairment, but others have found effects only for younger ages (10, 15). Given that the brain undergoes dynamic changes from the onset of puberty through early adulthood (37, 38), this developmental period should be the focus of future research on the age(s) at which harm occurs. Age of onset is a particularly important variable as it pertains to cannabis-induced cognitive impairment. I doubt cannabis is perfectly safe and harmless at any age, but it has consistently been shown to be both more harmful and less reversible to younger brains in development.