CHICAGO — New research suggests legalizing recreational marijuana for U.S. adults in some states may have slightly reduced teens’ odds of using pot.

One reason may be that it’s harder and costlier for teens to buy marijuana from licensed dispensaries than from dealers, said lead author Mark Anderson, a health economist at Montana State University.

Researchers analyzed national youth health and behavior surveys from 1993 through 2017 that included questions about marijuana.

Thirty-three states have passed medical marijuana laws and 11 have legalized recreational use — generally for ages 21 and up, many during the study years.