Marijuana may be 114 times less deadly than alcohol, but that doesn't mean it's without its negative consequences, per a study published today in the journal Hippocampus. Northwestern University researchers found that former teen potheads—more technically, those who lit up daily for roughly three years—had a hippocampus whose shape wasn't normal. The hippocampus plays a key role in long-term memory, and the study participants performed 18% worse on tests related to long-term memory as compared to their pot-free peers. While previous studies have arrived at those two findings independent of each other, this one linked the two. As for the hippocampus' shape, the study also noted that longer chronic use was tied to a more abnormal shape, explains a press release.
But the pool was on the small side, with 44 healthy controls and 10 participants who had what researchers term "cannabis use disorder": those who had begun daily pot use at age 16 or 17 (but did not abuse other drugs), continued that way for three years, then ceased using it for about two years. The same comparison was done on 28 young adults with schizophrenia and another 15 with schizophrenia who had the aforementioned pot history; in this case, the former potheads performed 26% worse. The lead study author concedes that "it is possible that the abnormal brain structures reveal a pre-existing vulnerability to marijuana abuse. But evidence that the longer the participants were abusing marijuana, the greater the differences in hippocampus shape suggests marijuana may be the cause." (On the subject of memory: Your 9/11 memories may be wrong.)