Fewer Pain Pill Overdoses In States With Legal Medical Marijuana

States that have legalized marijuana for medical use have lower rates of prescription painkiller overdose deaths than states that have not, new research suggests.

In a study published Monday in the latest issue of JAMA Internal Medicine , researchers found that although overdose deaths from opioid painkillers -- like OxyContin, Percocet and Vicodin -- have increased in the U.S. over the course of the last decade, they were 25 percent lower in states that implemented medical marijuana laws than other states. The reason for the association was unclear. The study was led by researchers from Johns Hopkins Bloomberg School of Public Health and the Philadelphia Veterans Affairs Medical Center.

"Prescription drug abuse and deaths due to overdose have emerged as national public health crises," Colleen L. Barry, senior author of the study and associate professor in the health policy and management department at the Bloomberg School, said in a statement. "As our awareness of the addiction and overdose risks associated with use of opioid painkillers such as Oxycontin and Vicodin grows, individuals with chronic pain and their medical providers may be opting to treat pain entirely or in part with medical marijuana, in states where this is legal."

The researchers used death certificate data compiled by the Centers for Disease Control and Prevention to determine the rate of opioid overdose deaths between 1999 and 2010 in all 50 states. They then took a close look at the states that had implemented medical marijuana laws during that same period.

By 1999, only three states had enacted medical marijuana laws -- California in 1996, and Oregon and Washington in 1998. By 2010, 10 more states had also passed medical cannabis laws. Nine additional states have legalized medical marijuana since 2010, but those states were not examined, as they were beyond the scope of the study date range.

The study reveals that states with legal medical marijuana had a 24.8 percent lower annual average painkiller overdose death rate than states without those laws. It also shows that in the years following the legalization of medical cannabis, the association was stronger over time -- in the first year of legalizing medical cannabis, painkiller overdose deaths were nearly 20 percent lower in states with the laws than without, and nearly 34 percent lower five years later, on average.

"It's important to note that this isn't a 25% decrease in rates, but a 25% lower rate than was expected," Dr. Marcus Bachhuber, the study's lead author and a Robert Wood Johnson Scholar at the Perelman School of Medicine at the University of Pennsylvania, told The Huffington Post.

About 60 percent of all opioid overdose deaths occur in patients who have legitimate prescriptions for the drugs, according to the CDC . In 2009, overdoses from prescription pain relievers resulted in the deaths of more than 15,000 people in the U.S.

"The proportion of people receiving prescription opioids to treat pain has almost doubled in the past 10 years," Bachhuber said. "Chronic or severe pain is the main reason for which people report taking medical marijuana in states that make this information public."

A growing body of research appears to suggest that marijuana use can be effective at pain relief. And while the drug is not without some health risks , in at least 10,000 years of human consumption , there have been no documented deaths as a result of marijuana overdose. While the cause of opioid overdose can vary from person to person -- due to strength of the dose and user tolerance levels -- a relatively small amount can lead to an overdose . By contrast, a marijuana smoker would have to consume 20,000 to 40,000 times the amount of THC in a joint in order to be at risk of dying, according to a 1988 ruling from the U.S. Drug Enforcement Administration.

It remains unclear exactly why this association exists between state medical marijuana laws and fewer opioid overdose deaths.

"During the study period, states were implementing a variety of policies to improve prescription painkiller safety, such as prescription monitoring programs, laws allowing pharmacists to request ID before giving out medications, and laws creating more oversight of pain management clinics," said Bachhuber. "We controlled for these policies, but it's possible that there were policies that we missed. Or, there might have been harder to measure changes such as increased awareness of and education about the issue of opioid overdoses, or changes in health trends, that were unrelated to medical marijuana laws but occurred in those states around the same time."

The researchers conclude in the study that although more investigation into the relationship between medical marijuana laws and fewer prescription narcotic overdose deaths is needed before specific policy conclusions can be formed, medical marijuana laws could one day be part of policies to prevent overdose.

"As more states pass these laws it will be important to continue collecting information and update our results," Bachhuber said. "On an individual level, I think many medical providers now struggle in figuring out what conditions medical marijuana could be used for, who would benefit from it, how effective it is, and who might have side effects; some doctors would even say there is no scientifically proven, valid, medical use of marijuana. There is definitely a need for more studies to help guide us in clinical practice."

The research was funded by grants from the National Institutes of Health's National Institute on Drug Abuse, the Center for AIDS Research at the Albert Einstein College of Medicine, the Robert Wood Johnson Foundation and the Philadelphia Veterans Affairs Medical Center.