Stoners who start smoking pot heavily before the age of 16 score significantly lower on cognitive tests than their non-toking counterparts—and worse than those who become stoners later in life, according to researchers. The average age of those studied was 22, and researchers defined a chronic marijuana user as someone who smoked pot at least 5 of the last 7 days and has smoked at least 3,000 joints in his lifetime, reports ABC News.
The study found chronic pot smokers repeated errors more often than the two other groups, even after researchers corrected them. They also had more trouble following rules, suggesting a problem with focus, researchers noted. "The findings were more striking than I anticipated," said lead researcher Staci Gruber. "Although the early onset smokers did the tasks faster than the other group, they made twice as many mistakes." People who start smoking young tend to smoke twice as often and three times the amount of marijuana than chronic smokers who start later in life, noted Gruber.