The agency estimates that every day 113 people die from drug overdoses in the United States, and another 6,700 land in the emergency room from an overdose.
Currently, 23 states allow medical marijuana to ease chronic pain and other conditions.
The researchers reviewed death certificates from all states between 1999 and 2010, when 13 states had legalized marijuana.
Since 2010, another 10 states and Washington, D.C., have adopted similar laws, the researchers said.
While overdose deaths have risen in all states, Bachhuber and his colleagues found that the annual average number of deaths caused by painkillers is nearly 25 percent less in states with medical marijuana laws.
"In absolute terms, states with a medical marijuana law had about 1,700 fewer opioid painkiller overdose deaths in 2010 than would be expected based on trends before the laws were passed," Bachhuber said.
States' overdose death rates decline an average 20 percent in the first year following the passage of a medical marijuana law, the researchers found. By the second year, overdose death rates on average decline 25 percent, and as much as 33 percent by five years after legalization of medical pot.
Medical marijuana laws also are associated with a more dramatic decrease in overdose death rates than other means commonly used to tackle prescription drug abuse, the study noted.
For example, prescription drug monitoring programs are associated with an average 3.7 percent increase in overdose deaths, compared with a 24.8 percent decline associated with medical pot legalization, according to the study.
Increased state oversight of pain management clinics is associated with a 7.6 percent decline in overdose deaths, while laws requiring patients to show ID when picking up a prescription are as
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