Democratic Sens. Bill Nelson (D-Fla.) and Brian Schatz (D-Hawaii) introduced legislation that would make it legal for military veterans to use medical marijuana.

The Veterans Medical Marijuana Safe Harbor Act filed on Wednesday would also allow Department of Veterans Affairs physicians to prescribe the drug "as a less harmful alternative to opioids in treating veterans."

"States with medical cannabis have a 24.8 percent lower mean annual opioid overdose mortality rate compared with States without medical cannabis laws," the bill reads.

If passed, medical cannabis would become legal under federal law for veterans to "use, possess, or transport medical marijuana in accordance with the laws of the State in which the use, possession, or transport occurs," according to the bill.

The bill would also require the VA to conduct research on "the effects of medical marijuana on veterans in pain" and the relationship between the use of cannabis and its effect on reducing opioid abuse among veterans.

What about the cost of research?

The bill calls for $10 million to be allocated to the VA for research on the effects of the cannabis on veterans' pain and $5 million for research on the effect on reducing opioid abuse among veterans.

The VA would have two years to complete the studies from the time the bill becomes law.

What else?

Thirty-one states, along with the District of Columbia, have passed laws allowing comprehensive medical marijuana use.

An additional 15 states allow the use of cannabidiol, or CBD, derived from hemp or cannabis but the extracts must contain zero to very low levels of THC, according to the National Conference of State Legislature.

Marijuana remains illegal under federal laws and is classified as a Schedule 1 substance under the Controlled Substance Act.

Research has been limited due to the prohibition of the drug.