Marijuana is legal for medical purposes in 33 states

Thirty-three states and Washington, DC, allow marijuana for medical purposes, although their approaches can significantly differ.

Some allow medical marijuana dispensaries and home cultivation. Others only allow home cultivation. And some allow dispensaries but not home cultivation.

There’s a growing body of research supporting marijuana’s use for medical purposes. Some studies and anecdotal evidence suggest marijuana can be used for various medical problems, including pain, nausea and loss of appetite, Parkinson’s disease, inflammatory bowel disease, PTSD (post-traumatic stress disorder), epilepsy, and multiple sclerosis.

But a review of the evidence from the National Academies of Sciences, Engineering, and Medicine found little evidence for marijuana’s ability to treat health conditions outside chronic pain, chemotherapy-induced nausea and vomiting, and patient-reported multiple sclerosis spasticity symptoms.

Several studies show legalizing medical marijuana dispensaries can lead to fewer opioid painkiller deaths, making medical marijuana one potential way to help fight the opioid epidemic. The rationale for this is simple: Studies show medical marijuana can effectively treat chronic pain, which opioids are commonly used for. But unlike opioids, medical marijuana cannot cause deadly overdoses. So medical marijuana could supplant some opioid use and save some lives.

Medical marijuana legalization also has a lot of popular support: A 2010 Pew Research Center survey found that 73 percent of American voters back medical marijuana, including 80 percent of Democrats, 76 percent of independents, and 61 percent of Republicans.

But the federal government doesn’t recognize marijuana’s medical potential, largely because the studies have been small so far, and there have been no large-scale clinical trials proving pot’s medicinal value.

Behind that judgment, though, lies a bit of a catch-22: It’s long been difficult to conduct thorough studies on the medical uses of marijuana because of the drug’s prohibition and the need for approval from a federal government that hasn’t been very interested in studying marijuana’s potential benefits. So the federal government is demanding scientific research proving marijuana has medical value, but the federal government’s restrictions make it difficult to conduct that research.

For legalization advocates, getting the federal government to acknowledge marijuana’s medical value could be a significant step forward. For one, it would push the Drug Enforcement Administration to reclassify marijuana from a schedule 1 to a schedule 2 substance, which could relax some of the restrictions on the drug. That alone would amount to a huge symbolic shift: After decades of scheduling marijuana in the strictest possible category, a downgrade could be taken as an acknowledgment by the federal government that its old policies have failed.