A new study indicates that cognitive function is impaired by chronic marijuana use. ("Chronic," like "frequent," you stoner.) Looks like your older brother was wrong when he told you that pot was harmless because "it's from the earth"!

Chronic marijuana smokers did worse on tests of cognitive function than non-smokers, and those who started smoking weed before age 16 did worse than the stoners who started later in life. Worse how? Chronic smokers "repeated errors more often than the two other groups, even after the authors corrected them," and "had more trouble maintaining a set of rules" and also "repeated errors more often than the two other groups, even after the authors corrected them."

But the thing is: The study defines "chronic" marijuana use as "smoking pot at least five of the last seven days" (which, well, [nervous laughter], that's just ridiculous, [tugs at collar], who would smoke that frequently) and "a minimum of 3,000 joints in a lifetime."

Three thousand joints! That's maybe not such a big deal to old hippies, but the average age of study participants was 22. So, participants who started smoking at age 18 would have had to smoke about two joints a day to be defined as "chronic," and those who started smoking at 16 would be sparking about 10 joints a week, every week, since that time. (How's that for cognitive function, science?) Which isn't impossible, obviously! But that's a rather high bar for "chronic," isn't it? [ABC News]