In addition, economic logic suggests that drug prohibition, whether for marijuana or any other drug, is misguided. Drug use entails risk for some users, and use sometimes harms innocent third parties. But the adverse effects of prohibition are far worse.

Little evidence suggests that prohibition reduces drug use. Instead, prohibition breeds black markets and pushes consumers into illicit drug use, which is far more dangerous than legal consumption. Drug quality control is poor in underground markets because reliable suppliers cannot legally advertise their goods and consumers cannot sue for damages due to faulty or mislabeled products. Drugs obtained from underground markets do not come with warning labels, and users cannot discuss safe use with their physicians, making them more likely to combine drugs with alcohol or other medications that suppress respiration.

Legalization opponents claim that drugs increase violent or criminal tendencies, but any association between drugs and violence arises mainly from prohibition’s impact on drug markets. Throughout the 20th century, major fluctuations in the U.S. homicide rate have been positively associated with fluctuations in the enforcement of drug and alcohol prohibition. Prohibition raises drug prices, which motivates some consumers to commit crimes to fund their drug use.

Under prohibition, drug‐​related disputes between users and suppliers, such as those over faulty or mislabeled products, are more likely to be settled with violence since they cannot be tried in court. Prohibition also decreases the marginal cost of committing a crime; a marijuana supplier who already evades the law has little incentive to obey the law in other instances. The Mexican drug war has also been linked to increases in homicide as captures of kingpins motivate rival gangs to exploit weakened organizations.

In addition, prohibition is expensive; the War on Drugs costs taxpayers around $50 billion annually, in addition to leaving a similar amount of tax revenue in the underground market. Prohibition reallocates law enforcement away from responding to violent offenses and increases civil liberties violations as police pursue perpetrators of victimless crimes.

The War on Drugs contributes to racial profiling and other racial disparities in law enforcement. Although black and white Americans use marijuana at roughly equal rates, blacks are nearly four times as likely to be arrested for marijuana possession. Prosecutors pursue mandatory minimum sentences for black defendants at twice the rate as for white defendants charged with the same offense. Criminalizing nonviolent and largely victimless behavior grants law enforcement substantial discretion in the interpretation and application of the law.

Prohibition has cost American taxpayers more than $1 trillion and has been largely ineffective in decreasing marijuana use. Worse, prohibition has created new risks to health and safety and has increased the incentive to engage in violence or crime. We should look forward to continued legalization of marijuana at the state and federal level.