Liberalization of medical marijuana and mental health in the USAThe approval of marijuana for medical use has had little effect on the mental health of the general population in the US. But legalization for therapeutic purposes does benefit those for whom it is intended. This is the conclusion of a study by researchers at the University of Basel. In the US, access to marijuana has been facilitated in most states since the mid-1990s - whether through medical clearance or through decriminalization of recreational use.