A study conducted by the American Journal of Epidemiology concludes that those who have used drugs casually—meaning occasionally or not heavily—in the past are not more forgetful, or stupider, than those who've never used drugs at all. The study involved 9,000 middle-aged adults in the UK. Participants were given cognitive and memory tests at the age of 42, and then again at the age of 50. Of the substances used by participants, marijuana was by far the most common; 6% had even used it in the past year. But amphetamines, LSD, hallucinogenic mushrooms, cocaine and ecstasy had also been taken. "Overall, at the population level, the results seem to suggest that past or even current illicit drug use is not necessarily associated with impaired cognitive functioning in early middle age," says lead researcher Alex Dregan of King's College, London. But don’t call your dealer just yet; the results shouldn't be seen as any incentive to use drugs, notes Harvard Medical School psychiatrist John Halpern: the study focused only on "casual" use, and doesn't rule out possible lasting side-effects of heavy or prolonged drug use.