By Keith Coffman
DENVER (Reuters) - The number of Colorado high school students who believe marijuana is harmful has fallen since the state legalized recreational pot, while teen use of the drug has declined slightly during the same time, health officials said on Thursday.
Colorado and Washington became the first U.S. states to legalize the possession and use of recreational marijuana by adults in ballot measures approved by voters in 2012.
Retail marijuana stores opened in Colorado on Jan. 1 and in Washington last month. Alaska, Oregon and the District of Columbia will vote on legalization initiatives in the fall.
The Colorado Department of Public Health and Environment said that in a survey it conducted of 40,000 teens, 54 percent believe use of the drug poses "a moderate to serious risk" to their health, down from 58 percent polled before the vote to allow recreational pot sales.
The survey found that one in five students admitted using marijuana within the last 30 days, down from 22 percent of those surveyed in 2011. One-third said they have tried pot.
Dr. Larry Wolk, the Colorado health department's chief medical officer, said in a statement that more young people will likely experiment with pot because of legalization.
But cigarette smoking by teens is declining at a faster rate than marijuana use, he noted, due to efforts to curb its use.
"As with tobacco, youth education prevention campaigns will help ensure adult legalization of marijuana ... does not impact the health of Colorado kids," Wolk said. "We know what works to protect young people from unhealthy substances."
Bob Doyle, chairman of the Colorado chapter of Smart Approaches to Marijuana (SAM), a group opposed to legalization, said his organization shares the health department's concerns about "the negative impact" pot is having on the state.
"The good news is the majority of communities in Colorado have a ban or moratorium on commercial marijuana businesses, and we hope that trend continues," Doyle said.
But Mason Tvert, spokesman for the pro-pot Marijuana Policy Project, said the poll shows that legalizing cannabis has worked to keep pot away from children.
"Once again, claims that regulating marijuana would leave Colorado in ruins have proven to be unfounded," Tvert said.
(Reporting by Keith Coffman; Editing by Daniel Wallis and Leslie Adler)