“There are a smattering of studies here and there, small studies that look at one type of substance use—for example, alcohol—but there really is not a single human study that comprehensively evaluates two things: 1) the risk of new onset substance use disorders across all major substances, and 2) harm reduction, or the question of do these drugs really reduce the risk of drug overdoses, drug deaths, drug-related hospitalizations, emergency room visits, and suicides,” says Al-Aly.