Often Wrong But Never in Doubt

(Marijuana map from governing. com)

In addition to taxes and regulations stunting sales, there may be another reason for business projections falling short where marijuana has been legalized: the public doesn't trust the enthusiasts who say it's no worse and may even be less harmful than alcohol.

Headline: Marijuana Is More Dangerous Than You Think. Coincident with the rise of marijuana use has been an increase in the incidence of psychosis and paranoia, though we must be careful to state that marijuana has not been proven to be the reason because correlation is not necessarily causation. [bold added]

And last September, a large survey found a rise in serious mental illness in the U.S. too. In 2017, 7.5% of young adults met the criteria for serious mental illness, double the rate in 2008.

None of these studies prove that rising cannabis use has caused population-wide increases in psychosis or other mental illness, although they do offer suggestive evidence of a link. What is clear is that, in individual cases, marijuana can cause psychosis, and psychosis is a high risk factor for violence. What’s more, much of that violence occurs when psychotic people are using drugs. As long as people with schizophrenia are avoiding recreational drugs, they are only moderately more likely to become violent than healthy people. But when they use drugs, their risk of violence skyrockets. The drug they are most likely to use is cannabis.

The most obvious way that cannabis fuels violence in psychotic people is through its tendency to cause paranoia. Even marijuana advocates acknowledge that the drug can cause paranoia; the risk is so obvious that users joke about it, and dispensaries advertise certain strains as less likely to do so. But for people with psychotic disorders, paranoia can fuel extreme violence. A 2007 paper in the Medical Journal of Australia looked at 88 defendants who had committed homicide during psychotic episodes. It found that most of the killers believed they were in danger from the victim, and almost two-thirds reported misusing cannabis—more than alcohol and amphetamines combined.

What about predictions that legalization would reduce violent crime?

The first four states to legalize marijuana for recreational use were Colorado and Washington in 2014 and Alaska and Oregon in 2015. Combined, those four states had about 450 murders and 30,300 aggravated assaults in 2013. In 2017, they had almost 620 murders and 38,000 aggravated assaults—an increase far greater than the national average.

The broad effects of legalization---public health and mental illness, criminal justice, economic activity, taxation--will take years to make themselves known.

But it's called a social experiment for a reason. We can guess at but don't know the results in advance. Possible harmful effects are already appearing. A little humility is called for, especially in the advocates, but I'm not expecting to see it.