A study published on September 15 shows that in states where medical marijuana is legal, fewer people use opioid drugs, bolstering advocates’ claims that marijuana can substitute for more deadly substances. 
Researchers examined federal traffic safety data from 1999 to 2013, using a sample of more than 68,000 people who died in a car crash in 18 states.
The study found that people were slightly less likely to test positive for opioids after a state had legalized medical marijuana, which in some areas of the country is prescribed in place of potent painkillers like oxycontin to treat severe or chronic pain.
Specifically, the researchers found an association between legalize medical marijuana and a decrease in testing positive for opioids after dying in a car crash, particularly among drivers aged 21 to 40.
In Montana, researchers observed a 1.7% reduction in the number of people who tested positive for opioids after the state’s medical marijuana law went into effect.
June H. Kim, a doctoral student at the Mailman School of Public Health, and the study’s lead author, said:
“We would expect the adverse consequences of opioid use to decrease over time in states where medical marijuana use is legal, as individuals substitute marijuana for opioids in the treatment of severe or chronic pain.” 
The researchers pointed out that the decrease was most notable among drivers aged 21 to 40, probably becausemost states with medical marijuana have age restrictions.
This is not the first time medical marijuana laws have been linked to lower rates of opioid use. For example, a paper published earlier this year found that Medicare Part D prescriptions for painkillersdropped significantly in states where medical marijuana is legal. 
Past studies have shown that fewer people die of opioid overdoses in states with medical marijuana laws than in states without them. Access to medical cannabis dispensaries has also been linked to lower rates of opioid overdose and death.
The mounting evidence has at least one drug maker worried. Insys Therapeutics, a drug company that solely produces fentanyl, a drug many times stronger than heroin, recently donated $500,000 to a campaign fighting a proposition in Arizona that would legalize recreational marijuana. Insys also has a history of legal problems,.
Keep in mind that a dose of fentanyl the size of a grain of salt is enough to kill someone. That’s why doctors prescribe it by the millionth of a gram. The drug is so dangerous that some police officers carry an antidote … in case they touch it.  
This article originally appeared at Natural Society.