Those who oppose medical marijuana legislation often cite the strong association between marijuana use and criminal activity. This includes the US federal government, which continues to

classify marijuana as a schedule one drug. We analysed city-level data from states across the US and found that medical marijuana laws have little effect on violent or property crime in

nearly all medical marijuana states. In the case of California, the crime rates actually show a substantial decrease of around 20%. ------------------------- _ READ MORE: MEDICAL CANNABIS

USERS COULD STILL BE CRIMINALISED IN UK DESPITE GOVERNMENT ACCEPTING ITS BENEFITS _ ------------------------- A NATURAL EXPERIMENT Medical marijuana laws represent a major change in

marijuana use from spurious correlations because of individual heterogeneity. Individuals who choose to use marijuana are likely different from those who don’t. The passage of medical

marijuana laws offers researchers a good natural experiment to study the causal effects of marijuana use on a variety of health outcomes, including drunk driving, hard drug use and opioid

painkiller use. USERS AND CRIME The perception that marijuana use leads to crime can be traced back to the 1930s. In an effort to gain public support for marijuana prohibition, the Narcotics

Bureau chief Harry Anslinger collected dubious anecdotes of marijuana causing crime and violence in his infamous Gore Files. ------------------------- _ READ MORE: RE-CRIMINALIZING CANNABIS

IS WORSE THAN 1930S 'REEFER MADNESS' _ ------------------------- There is indeed a strong correlation between marijuana use and criminal activity. For example, the Arrestee Drug

Abuse Monitoring Program shows that more than half of adult male arrestees tested positive for marijuana use. Financial needs can lead to property crime for some heavy users. Research also

shows that long-term neuropsychological effects of marijuana can harm the brain, causing violent behaviours. Some studies have identified brain abnormalities in MRI images among casual and

abstinent users. Nevertheless, such correlation could be entirely spurious because marijuana users have a higher propensity to commit crimes. Only people who are willing to break laws would

use marijuana under prohibition. EFFECTS OF MEDICAL MARIJUANA LAWS ON CRIME In our paper, we used data on criminal offence, spanning more than 25 years (1988–2013). We analysed relatively

large cities with at least 50,000 residents. In addition to traditional regression analysis, we adopted the state-of-the-art synthetic control method that allows us to estimate the effects

of medical marijuana laws in each city. To make cities with and without medical marijuana laws comparable, we created a synthetic city from a pool of cities without medical marijuana laws.

That way the pre-law crime rates in the synthetic city and the city of interest are as close as possible. We then used the post-law crime rate in the synthetic city as an estimate for the

medical marijuana city’s counterfactual crime rate – the rate you would expect if the medical marijuana law had not been passed. The difference in post-law crime rates between the synthetic

city and the medical marijuana city is the causal effect of medical marijuana law on crime. We found that the actual crime rates in medical marijuana cities generally move closely with the

synthetic cities. This suggests no substantial effect on both violent and property crime. The results remain similar when we look at specific crimes such as murder, rape, robbery, aggravated

assault, burglary and theft. Our findings show that we can safely rule out that medical marijuana laws and the associated marijuana use cause increased crime. The strong correlation between

marijuana use and criminal activity is mostly spurious. CALIFORNIAN EXPERIENCE Violent and property crime rates dropped by 20% since California passed medical marijuana legislation more

than two decades ago. It was reported that there are more marijuana dispensaries than Starbucks or McDonalds in cities like Los Angeles. California’s medical marijuana law may have shrunk

the marijuana black market and its associated violence. It may have helped to reallocate police resources towards deterring crime instead of enforcing drug laws. The presence of dispensaries

may also deter crime. They are required to deal in cash and thus invest heavily in security. Another study found a similar decrease in violent crime in states bordering Mexico, including

California. It argues that medical marijuana legislation reduced crime associated with drug trafficking through Mexican cartels. The US experience suggests that most stigmas associated with

marijuana use are not supported by empirical evidence. Although medical marijuana laws increase heavy marijuana use among non-patients, they do not lead to negative social outcomes. Our

study provides robust evidence that medical marijuana legislation does not contribute to crime, and possibly helps to reduce it. This conclusion may relieve a major concern for countries

considering to legalise medical marijuana, including New Zealand and Canada. The US experience is unique, especially because of its war on drugs. But the main conclusion that increased

marijuana use does not cause more crime likely applies in other countries.