Anti-drug bureaucrats unveiled findings from the 2013 Monitoring the Future survey Wednesday. The large-scale drug use questionnaire found declining rates of drug, alcohol and tobacco use among teens – and also a virtually nonexistent year-to-year change in marijuana use.

That's despite a dramatic bump in public support for marijuana legalization and the forthcoming opening of recreational marijuana stores in Colorado and Washington in early 2014.

Nora Volkow, director of the National Institute on Drug Abuse, said on a conference call with reporters that NIDA will carefully study trends in the two states, where adults over age 21 will be able to shop for pot.

Volkow said the policy changes may "translate pretty rapidly" into schoolroom performance. Emergency room entries and car accidents also will be looked at, she said.

But Volkow cautioned there may be somewhat of a chicken-or-egg dilemma. Colorado and Washington residents, she said, almost certainly view marijuana as less harmful than residents of states that have not legalized the drug. Higher statewide acceptance of marijuana – as displayed in 2012 referendum votes – rather than official legalization, could translate to higher teen use, she said.

The drug use survey, administered by University of Michigan researcher Lloyd Johnston, polled 45,449 students in three grades – eighth, 10th and 12th – at 395 public and private schools.

Although the perceived risk of marijuana declined significantly, daily teen use of marijuana remained stable at 6.5 percent among 12th-grade students and 1.1 percent among eighth-graders. Among 10th-grade students, self-reported daily use ticked up from 3.5 to 4 percent.

A table on the NIDA website shows there has been no statistically significant year-to-year change in daily, weekly, monthly or lifetime marijuana use rates since 2010 in any of the three age groups.

But Johnston warned "[a decline in] perceived risk has become a leading indicator of things to come." Lloyd said perceived risk has been "going down rather sharply" for marijuana.

In the past year, the percentage of 12th-grade students viewing marijuana use as harmful dropped from 44.1 percent in 2012 to 39.5 percent in 2013. There was a similar decline in the other age groups.

"These discussions [about legalization] are nationwide," Johnston said. "When two states legalized [marijuana] that was an issue that was carried throughout the country and youngsters throughout the country were exposed to the discussion and the issues." He said it's inconceivable successful legalization drives would not lower perceptions of risk.

A poll released Oct. 22 by Gallup put nationwide support for marijuana legalization at 58 percent.

Gil Kerlikowske, director of the Office of National Drug Control Policy since 2009, blamed the shift in public opinion on Congress for not funding anti-marijuana ad campaigns included in the past two years of President Barack Obama's spending proposals.

"Without funding it's very difficult to get that message out," he said.

"Clearly these two states are engaging in a very large social experiment," Kerlikowske warned, "and as much of the information we're beginning to see portends, they're going to have a very difficult time."

Kerlikowske said his office would provide the Department of Justice, which will allow states to regulate marijuana in violation of federal law pursuant to various restrictions, with data on the effects of legalization in Colorado and Washington..

Obama's "drug czar" also bashed medical marijuana policies.

"The promise in medical marijuana states to the voters was that there would be regulatory schemes to prevent marijuana from falling into the hands of young people," he said. "In every state that promise has clearly been broken."

A small percentage of teenagers who use marijuana said in the survey they had a medical prescription, and others said they acquired marijuana from someone using it for medical purposes. In some states, the age for medical marijuana is 18. In the two legalization states, the marijuana age limit is 21.

Mason Tvert of the Marijuana Policy Project recommended that anti-drug officials keep an open mind about legalization.

"Those selling marijuana in the underground market are not asking for ID," Tvert said in a statement. "By regulating marijuana like alcohol and cigarettes and enforcing similar age restrictions, we would very likely see a similar decrease in availability and use among teens."