A study last year found that young adults who’d smoked marijuana daily as teens performed worse on memory tests than non-smokers, even though they’d quit two full years before. (They even had differently shaped brains.) The effects were bigger in people who’d started smoking younger. Other studies. however, have shown that brain function returns to normal after a month of abstinence, however.  It’s worth toking that with a grain of salt.

MORE: Pot and Memory Loss