In this Feb. 7, 2014 file photo, a worker cultivates a special strain of medical marijuana known as Charlotte's Web inside a greenhouse, in a remote spot in the mountains west of Colorado Springs, Colorado.

(AP Photo/Brennan Linsley)

A national study says Colorado had the second-highest number of regular marijuana users as the state began legalizing the drug.

The Denver Post reported that the study by the National Survey on Drug Use and Health found about 1 out of 8 Colorado residents older than 12 had used marijuana in the past month. The study says only Rhode Island topped Colorado in the percentage of residents who reported using pot as often.

The numbers are among the first to quantify marijuana use in Colorado since pot possession and use became legal for those over 21. But they don't include data from 2014, when recreational marijuana shops opened.

University of California, Los Angeles, professor Mark Kleiman says the study does not say much about the long-term effects of legalization.