Previous studies have found links between cannabis use and increased prevalence of mental disorders, but researchers don’t know if marijuana caused the disorders or if it was simply a matter of people who are prone to mental disorders seeking out alternative treatments, such as cannabis. Another claim made by the study was that evidence was found of the so-called “gateway” theory, the theory that cannabis use leads people to harder drug use down the line. If marijuana were truly a gateway, wouldn’t the number of hard drug users be closer to the number of regular marijuana users?