A new study is putting a closer spotlight on whether medical marijuana could be the answer to rising opioid deaths. 

The results, published Monday in the Proceedings of the National Academy of Sciences of the United States of America, expanded on data released in 2014. 

The original study compounded statistical data from 1999 through 2010. Those numbers showed evidence that state medical cannabis laws were associated with lower-than-expected opioid overdose mortality rates from 1999 to 2010.

Now, researchers have expanded on that study, using the same methods, but entering data through 2017. The expanded research showed the opposite trend. 

From 2010 through 2017 states with legalized medical marijuana saw an increase in opioid deaths. For those data sets, states that had legalized medical marijuana saw an increase of over 22% in overdose deaths. 

Dr. Chelsea Shover Ph.D., a postdoctoral researcher at Stanford University, and one of the authors of the study says it's not surprising. 

"So, we the authors, do not think that it was saving people ten years ago and it's killing people now. Rather, we say that this is pretty good evidence that medical cannabis doesn't really seem to affect a population level," Shover said. 

For Shover, it's proof that while there's an increasing number of states approving legalized medical marijuana, there's no causal relationship between medical pot and opioid overdoses. 

"If we look at this association again in five or ten years, I think you're still going to find something that's consistent. I mean, these two things are happening at the same time, but they're just not causally related," she said. 

Which is why she's hoping lawmakers will change the way they talk about "solutions" to the opioid epidemic. Shover said she has heard countless lawmakers pledge to legalize medical marijuana to curb the rate of opioid deaths. 

"It makes sense to focus on both of them, but not to link them with one as a solution to the other,' Dr. Shover continued. 

"I hope that the takeaway from this one study is that policymakers just focus less on talking about how medical cannabis might be some sort of silver bullet. Because we in the research world, we know it's not," she explained. "And we knew it before we did the study, but we did it to show, 'Hey this is something a lot of us would love if it were true.' I wish it were. But it just doesn't seem to be."

She's hoping that the study will prove that medical marijuana does not impact opioid deaths, and will help toward the conversation toward other solutions. "It's just that when we're thinking about how to combat the opioid overdose epidemic, we need to be thinking about strategies that really do work," she said. 

Even with increasing use of medical marijuana, Shover said the percentage isn't enough to curb the sheer number of overdose deaths. 

"At a population level about two and a half percent of the U.S. population, according to a pretty good estimate, uses medical cannabis. So we don't think it's plausible that that small of a percentage would alter the population overdose mortality.," she explained. "It's not enough people to believably have that effect. Even though it might be technically possible, it just doesn't seem likely." 

However, Dr. Shover said there's a place for medical marijuana in the conversation and most notably in research. 

"All that said, there is some emerging evidence about potential uses for medical cannabis even related to opioid-use disorder. There's a good study that just came out of Yasmin Hurd's lab at Mt. Sinai about the administration of CBD to reduce heroin cravings. That's a really small study, and there's a long way to go before that becomes something that can affect a population level, but it is promising," Shover said.  "So we're not saying that medical cannabis is all bad because it's not. We have several FDA approved drugs based on it. We have lots of reports from patients that say it helps them. And that's all good stuff.

Especially as more of states move to decriminalize and as the research that's out there now gets closer to findings that we can use to improve public health. There are a few medical uses of cannabis that have been shown through rigorous research and demonstrated to really work, and there are other potential ones that are being studied now. I think we'll just be learning more, and that's great."

As with most scientific research, Shover said there's still work to be done to learn more.