The density of licensed marijuana retailers is associated with more use and a greater intensity of use among young adults, according to a study in Los Angeles County.

Researchers at the RAND Corporation studied young adults in Los Angeles County the year before and the year after marijuana became available for recreational purchase in retail shops in California. They found young adults who had a higher number of licensed marijuana outlets within four miles of their home were more likely to have used marijuana in the past month, HealthDay reports.

The study also looked at unlicensed retailers, and found they made up 62% of all outlets. Young adults in neighborhoods with a greater density of unlicensed outlets had an increased likelihood of daily or near-daily marijuana use. They also were more likely to use greater amounts of marijuana and to show symptoms of cannabis use disorder, the researchers reported in the American Journal on Addictions.