Each of these four legalizations occurred recently, and each rolled out gradually over several years.
Our analysis compares the pre‐ and post‐policy‐change paths of marijuana, other drug or alcohol use, marijuana prices, crime, traffic accidents, teen educational outcomes, public health, tax revenues, criminal justice expenditures, and economic outcomes.
We conclude that state‐level marijuana legalizations to date have been associated with at most modest changes in marijuana use and related outcomes.
Particularly striking is the absence of significant adverse consequences from legalization, given the sometimes dire predictions made by legalization opponents. In the aftermath of legalization, crime has not soared. Road accidents show no significant uptick. Emergency treatment center admissions remain steady. Marijuana use, while still on an upward trend, displays no acceleration. And use of harder substances actually begins to trend downwards, suggesting that the “gateway” phenomenon has not materialized.
Our analysis does not, by itself, determine whether legalization is wise policy. Ardent critics can assert that increased misuse and other unwanted side effects will boom after more time has passed; our results cannot address this assertion. Alternatively, critics sometimes argue against legalization based on ethical, religious, or moral claims, independent of measurable outcomes.
Most critics, however, have based their opposition on claims that legalization will unleash rapid and dramatic increases in marijuana use and the possible adverse consequences of that use. Our study reveals no substantial evidence that supports these strong hypotheses.
A different question is whether legalization proponents should have to prove marijuana’s safety beyond all doubt before it can become legal. The answer should be obvious: no one has ever required advocates of legal alcohol, tobacco, automobiles, downhill skiing, or triple‐cream cheeses to prove beyond all doubt that these goods do not, sometimes, have serious long‐term consequences. In fact, each of these, plus innumerable other goods and services, can harm those who consume them, or others, when misused.
But in a free society, the presumption must be that every good, service, action or activity is legal except when compelling evidence shows that use causes substantial harm to innocent third parties and that the costs of regulation or prohibition are smaller than those of the goods or actions themselves. Our research, like that of many others, suggests that no such case exists for marijuana.