Another state has legalized medical marijuana.

This time, West Virginia became the 29th state to allow cannabis for medicinal purposes after Gov. Jim Justice signed a bill passed by the legislature into law.

West Virginia’s medical marijuana measure is more limited than many other states’ laws. It will allow vaporization, along with pills, oils, gels, creams, ointments, tinctures, and other liquids. But it doesn’t allow smoking pot, and it doesn’t allow dispensaries to sell edibles. Qualifying conditions include terminal illnesses, cancer, HIV/AIDS, epilepsy, PTSD, and severe pain — all of which are standard for state medical marijuana laws. (Marijuana Policy Project, a pro-legalization group, has a broader rundown of the law.)

There’s evidence for marijuana’s medical use

A recent review of the research, from the National Academies of Sciences, Engineering, and Medicine, found that marijuana is promising for chronic pain, multiple sclerosis, and cancer patients.

The evidence for other medical conditions is weak. That’s not necessarily because pot isn’t effective for those conditions, but because the research is simply nonexistent or lacking. One big reason for that: The federal prohibition on marijuana has for years imposed harsh regulatory hurdles on research on pot — largely allowing studies into pot’s risks but not its benefits. That’s made it difficult for researchers to get a better grasp of the drug’s potential medical benefits.

Despite the limited research, more than half the states have passed medical marijuana, buoyed by popular support for cannabis’s medical use and the goal to provide at least some relief for patients now based on the limited and anecdotal evidence for pot.

Medical marijuana can provide some relief in the opioid epidemic

There is one sense of urgency to medical marijuana legalization: It could help combat the opioid epidemic. Studies suggest marijuana can effectively treat chronic pain, which opioids are commonly prescribed for. Meanwhile, there is no good evidence that opioids can treat chronic pain, while there’s a lot of evidence for opioid’s long-term risks, like addiction, overdose, and even increased pain (known as “hyperalgesia”).

But unlike opioids, medical marijuana cannot cause deadly overdoses. So if some pain patients shift over to marijuana from opioids once pot is legal, it could save some lives. Indeed, the research suggests that states with laxer medical marijuana laws have fewer opioid deaths than they otherwise would.

West Virginia is the state hit hardest by the opioid epidemic, with the highest opioid overdose death rate of any state in the country. That makes it all the more urgent for the state to try different ideas to combat the epidemic, including medical marijuana.

For more on the opioid epidemic, read Vox’s in-depth explainer, the abridged version, or the maps and charts version.

Watch: The opioid epidemic, explained