States around the country — 29 of them, plus Washington DC — have legalized medical marijuana.

The American public largely supports the legalization of medical marijuana. At least 84% of the public believes the drug should be legal for medical uses, and recreational pot usage is less controversial than ever, with at least 61% of Americans in support.

Even though some medical benefits of smoking pot may be overstated by advocates of marijuana legalization, recent research has demonstrated that there are legitimate medical uses for marijuana and strong reasons to continue studying the drug's medicinal uses.

Even the NIH's National Institute on Drug Abuse lists medical uses for cannabis.

There are at least two active chemicals in marijuana that researchers think have medicinal applications. Those are cannabidiol (CBD) — which seems to impact the brain without a high— and tetrahydrocannabinol (THC) — which has pain relieving properties and is largely responsible for the high.

But scientists say that limitations on marijuana research mean we still have big questions about its medicinal properties. In addition to CBD and THC, there are another 400 or so chemical compounds, more than 60 of which are cannabinoids. Many of these could have medical uses. But without more research, we won't know how to best make use of those compounds.

More research would also shed light on the risks of marijuana. Even if there are legitimate uses for medicinal marijuana, that doesn't mean all use is harmless. Some research indicates that chronic, heavy users may have impaired memory, learning, and processing speed, especially if they started regularly using marijuana before age 16 or 17.

For some of the following medical benefits, there's good evidence. For others, there's reason to continue conducting research.

Jennifer Welsh contributed to an earlier version of this story.

The best-supported medicinal use of marijuana is as a treatment for chronic pain.

A recent report by the National Academies of Sciences, Engineering, and Medicine said there was definitive evidence that cannabis or cannabinoids (which are found in the marijuana plant) can be an effective treatment for chronic pain.

The report said that is "by far the most common" reason people request medical marijuana.

There's also strong evidence medical cannabis can help with muscle spasms.

That same report said there's equally strong evidence marijuana can help with muscle spasms related to multiple sclerosis.

Other types of muscle spasms respond to marijuana as well. People use medical marijuana to treat diaphragm spasms that are untreatable by other, prescribed medications.

It doesn't seem to harm lung capacity, and may even improve it.

There's a fair amount of evidence that marijuana does no harm to the lungs, unless you also smoke tobacco. One study published in Journal of the American Medical Association found that not only does marijuana not impair lung function, it may even increase lung capacity.

Researchers looking for risk factors of heart disease tested the lung function of 5,115 young adults over the course of 20 years. Tobacco smokers lost lung function over time, but pot users actually showed an increase in lung capacity.

It's possible that the increased lung capacity may be due to taking a deep breaths while inhaling the drug and not from a therapeutic chemical in the drug.

The smokers in that study only toked up a few times a month, but a more recent survey of people who smoked pot daily for up to 20 years found no evidence that smoking pot harmed their lungs, either.

The National Academies report said there are good studies showing marijuana users are not more likely to have cancers associated with smoking.