The legalisation of marijuana for medical purposes has led to a significant reduction in violent crime in several US states bordering Mexico, according to new research.

The study, published in The Economic Journal, found that the rate of violent crime – including robberies, murders and aggravated assaults – fell by 12.5 per cent in counties close to the border after the introduction of medical marijuana laws (MMLs).

“MMLs allow people to grow and cultivate marijuana plants legally within the US,” Professor Evelina Gavrilova, one of the study’s authors, told The Independent.

“This means that people don’t need to buy illegal marijuana anymore so drug trafficking organisations (DTOs) have far fewer customers.”