Marijuana is sold legally at a dispensary in California.
Credit: Mathew Sumner/AP

The introduction of medical marijuana laws has led to a sharp reduction in violent crime in US states that border Mexico, according to new research.

According to the study, Is Legal Pot Crippling Mexican Drug Trafficking Organizations? The Effect of Medical Marijuana Laws on US Crime, when a state on the Mexican border legalised medical use of the drug, violent crime fell by 13% on average. Most of the marijuana consumed in the US originates in Mexico, where seven major cartels control the illicit drug trade.