DENVER — Colorado emerged as the state with the second-highest percentage of regular marijuana users as it began legalizing the drug, according to a new national study.

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. Only Rhode Island topped Colorado in the percentage of residents who reported using pot as often, according to the study.

The study averaged state-specific data over two-year periods. It found that, for the 2011-2012 period, 10.4 percent of Colorado residents 12 and older said they had used pot in the month before being surveyed. That number jumped to 12.7 percent in the 2012-2013 data. That means about 530,000 people in Colorado use marijuana at least once a month, according to the results.

Nationally, about 7.4 percent of people 12 and older reported monthly marijuana use. That’s an increase of about 4 percent.

In Washington state, which also legalized marijuana use and limited possession for adults, monthly pot use rose about 20 percent to 12.3 percent of people 12 and older.