As of June, a total of 31 states and the District of Columbia allow for the use of medical marijuana. Pain is the most common reason people say they need cannabis and the vast majority of users say that it helps. However, despite the claims of the many individuals who believe that cannabinoids — the chemicals in marijuana — can ease pain, it’s been difficult for scientists to explain why. Researchers published in JAMA Psychiatry now claim to clarify the discrepancy.

In a systematic review and meta-analysis released Wednesday, scientists from Syracuse University explain that while studies can’t currently prove that cannabinoid drugs reduce pain, research does demonstrate that they can help with the experience of feeling pain. An evaluation of 18 studies that included 442 adults revealed that the use of cannabinoid drugs modestly increased people’s threshold for pain and reduced pain’s overall sensation of unpleasantness. This suggests to the researchers that cannabis’ analgesic properties, or its ability to relieve pain, affect the mind rather than the body.

“This [result] is especially salient because managing chronic pain is not solely about minimizing pain,” Kevin Boehnke, Ph.D., who was not involved in the study, tells Inverse. Boehnke is currently a part of a University of Michigan study also analyzing the effect of cannabis on chronic pain. “Sleep problems, fatigue, anxiety, depression, and other factors tie into the experience of chronic pain.”

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Scientists are exploring why people feel like marijuana reduces pain.

But because these studies all focused on laboratory-induced pain, we can’t infer whether the results will hold in people who actually have chronic pain, Boehnke says. Pain is a complex phenomenon with multiple dimensions, and in studies on clinical populations who use marijuana to treat pain, it’s been difficult to tell what’s actually helping them. Surveys of people who use cannabis for chronic pain haven’t had much luck proving it helps either. In a paper published in The Lancet in July, scientists found that people who used cannabis felt more pain than those who didn’t, but there was “no evidence that cannabis use improved patient outcomes.”

Lead author and doctoral candidate Martin De Vita tells Inverse that while there is a desperate need for more studies that examine clinical pain conditions, clinical pain “is often accompanied by comorbid conditions, like anxiety or depression, which can also influence pain.”

“Experimental studies that induce pain the laboratory are great because they can be highly controlled and can test the effects of cannabinoid administration on specific pain processes,” De Vita says. “When we see effects from cannabinoids in experimental pain studies, we are more confident that cannabinoids are the cause.”

From these studies, De Vita and his colleagues determined that cannabinoids may provide relief by improving the emotional component of pain (unpleasantness), rather than by reducing the intensity of that pain.

“This may underlie our other finding that participants were able to tolerate pain better after cannabinoids were administered,” De Via says. “So while conventional wisdom was ‘cannabinoids relieve pain,’ it is now ‘cannabinoids may relieve specific aspects of pain.’”

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Cannabidiol (CBD) is a different cannabinoid than THC. 

The authors also say that because the studies focused on the “feel-good” cannabinoid tetrahydrocannabinol (THC) and not other cannabinoids, like cannabidiol (CBD), it’s currently unclear whether other varieties would have different effects on pain.

Boehnke also points out that the doses of THC used in these studies aren’t necessarily representative of the herbal cannabis available to many people today, medical or not. Different strains of cannabis have different THC levels, and what a person out in California or Colorado has the opportunity to buy is very different than what a researcher can get their hands on. Federally, marijuana is still a Schedule I drug.

“This systematic review highlights the necessity of loosening restrictions on cannabis research — such as rescheduling cannabis and cannabinoids to Schedule II — so that science catch up with policy,” Boehnke explains. “We’re in such a bizarre place right now societally. You can go buy hemp oil that contains CBD from Amazon or a local supermarket, but to try to use those compounds in clinical studies requires an immense regulatory burden.”