Despite being marketed as harmless, the hard data about marijuana paint a different picture. For instance, a global survey found that only 64% of 50,000 cannabis users believed the drug could cause dependence,63 meaning that 36% of active users did not know they had a 10% chance of becoming addicted.64 And that’s the conservative estimate—another study found that approximately 3 in 10 people using cannabis products met the criteria for marijuana use disorder.65
The CDC warns that “people who use marijuana are more likely to develop temporary psychosis (not knowing what is real, hallucinations, and paranoia) and long-lasting mental disorders, including schizophrenia (a type of mental illness where people might see or hear things that are not really there).”66 A host of studies and health agencies has confirmed this alarming connection. The National Institute on Drug Abuse warns, “Recent research suggests that smoking high-potency marijuana every day could increase the chances of developing psychosis by nearly five times compared to people who have never used marijuana.”67 The connection between psychosis and heavy marijuana use is especially frightening when we consider that about 20% of cannabis users consume it almost daily.68 As Dr. Tyler J. VanderWeele of Harvard University summarized, “Cannabis use disorder is not responsible for most schizophrenia cases, but it is responsible for a nonnegligible and increasing proportion.”69
Even irregular use of marijuana leads to negative effects. One study found that adolescents who occasionally used marijuana were at greater risk of using illegal drugs and developing alcohol and tobacco dependence.70 Another study found that those who started using marijuana in their teens experienced a drop in IQ, even if usage was not regular, while nonusers saw a small rise in IQ. These researchers also found that the greater the cannabis use, the greater the decline, with losses of up to eight IQ points.71
To make matters worse, the IQ decline for those who began consuming marijuana as teens persisted even after drug use stopped.72 Likewise, one study that tracked college students found that those who used marijuana just twice a month were 11% more likely to be “discontinuously enrolled”—to permanently drop out or to leave college for multiple semesters but eventually return— than students who were basically nonusers.73 Additionally, the National Academies of Sciences, Engineering, and Medicine found an association “between cannabis use and increased incidence of suicidal ideation and suicide attempts, with a higher incidence among heavier users.”74
Not long after the recreational sale of marijuana began in Colorado, Pope Francis prophetically said, “Attempts, however limited, to legalize so-called ‘recreational drugs,’ are not only highly questionable from a legislative standpoint, but they fail to produce desired effects.”75 As the pope predicted, legalization has produced unintended, harmful effects. One study that tracked UCHealth University of Colorado Hospital found marijuana-related emergency room visits tripled after the sale of recreational marijuana began in January 2014.76 Issues ranged from cannabis hyperemesis syndrome (uncontrolled bouts of vomiting) to acute psychiatric symptoms to cardiovascular problems.77 As previously mentioned, marijuana use disorder now enslaves 3.3% of the state’s population, as compared to 1.6% in the early 2000s.78 This is not surprising since Coloradans’ cannabis use has increased dramatically since legalization: the latest data show a 26% increase since 2013.79 In practice, more people using marijuana inevitably means more addiction.
Increasing cannabis use has also ballooned other problems. Marijuana-related DUIs in the state numbered 676 in 2014 but spiked to 1,513 in 2020.80 This is consistent with the finding of the National Academies of Sciences, Engineering, and Medicine that “there is substantial evidence of a statistical association between cannabis use and increased risk of motor vehicle crashes.”81 Tragically, traffic deaths involving drivers who tested positive for marijuana more than doubled from 55 in 2013 to 131 people killed in 2020. Whereas before legalization cannabis-related traffic fatalities made up 11% of all traffic deaths, now they represent 21%.82 In a similarly heartrending vein, statistics show 105 Coloradans with marijuana in their systems committed suicide in 2013, whereas in 2019 that number more than doubled to 236 (representing 29% of all suicides, up from 14% in 2013).83 “An analysis of survey data from more than 280,000 young adults ages 18–35 showed that cannabis use was associated with increased risks of thoughts of suicide (suicidal ideation), suicide plan, and suicide attempt.”84 It is our hope that the abundance of harmful effects will give even the most ardent defenders of legalization pause.