Technically speaking, its THC—the cannabinoid that gets you high—which is illicit. When you take a drug test, the aim is to detect THC in your body, not “cannabis.” If you possessed weed without any THC in it, technically you wouldn’t be in violation of the law. Because “weed” without THC has a different name: hemp. And the rules governing hemp are quite different from the restrictions placed on cannabis.
There is reasonable evidence from prospective epidemiological studies which suggests that cannabis use can precipitate schizophrenia in persons who are vulnerable because of a personal or family history of schizophrenia. There is also evidence that a genetic vulnerability to psychosis increases the risk that cannabis users will develop psychosis (McGuire et al., 1995; Arseneault et al., 2002; Verdoux et al., 2002). A casual relationship also has biological plausibility in that the cannabinoid and dopaminergic neurotransmitter systems interact in animals. D'Souza and colleagues (1999) have shown in a provocation study that THC produces a dose-dependent increase in psychotic symptoms under double-blind placebo conditions; and Caspi and colleagues (2005) have shown an interaction between specific alleles of the COMT allele and psychotogenic effects of cannabis. If these results can be replicated and extended, they will increase the likelihood that cannabis can be a contributory cause of psychosis in vulnerable individuals.
Cannabis use started to become popular in the United States in the 1970s. Support for legalization has increased in the United States and several U.S. states have legalized recreational or medical use. A 2018 Social Science Research study found that the main determinants of such changes in attitudes toward marijuana regulation since the 1990s were changes in media framing of marijuana, a decline in perception of the riskiness of marijuana, a decline in overall punitiveness, and a decrease in religious affiliation.