More college students are getting high on pot, and those who do smoke are getting stoned more frequently, according to the national Monitoring the Future study.
The number of students who say they have used marijuana in the past 12 months jumped from 30 percent in 2006 to 38 percent in 2015, while other drug use is on the decline, say researchers who have been tracking college students since 1980.
The most startling trend is the number who smoke daily: One in every 22 college students surveyed said they toked up at least 20 times in a month.
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And two-thirds say they believe a little weed every now and then is safe.
"Something has changed dramatically," said principal investigator Lloyd Johnston, a distinguished senior research scientist at University of Michigan. "We've been asking the same question for years, and their answers are changing."
Johnston says the medical marijuana movement and legalization of recreational use in four states has set the stage for more lax attitudes.
"It's become a national phenomenon, not specific to any one state," he told NBC News.
Colorado, Oregon, Washington and Alaska, as well as the District of Columbia, have fully legalized pot and regulate its growth and sales. Several other states, including California and Nevada, may soon follow.
College students in states where weed is legal at age 21 say they are not surprised by the new numbers. They asked NBC News to identify them by their first names only for fear they could face professional or legal repercussions for their comments.
"There is a lot of marijuana usage at my school, but I'm not sure that has changed much since legalization in this state because it's pretty strongly part of the culture and has been for a long time," said Aidan, a 21-year-old evolutionary biology major from Evergreen State University in Olympia, Washington.
"I just hope they start drinking less as they smoke more," Aidan told NBC News. "A group of stoned kids is a lot less dangerous than a group of drunk ones."
Mckenna, 18, who is from Colorado and is now a freshman and art major at the University of New Mexico, said, "Pot smoking has always been common among students."
"I think pot being legalized makes people think it is safer because the government allows its use," she told NBC News. "But that doesn't mean you should smoke every day and become a lazy stoner who eats pizza 24/7."
Both students said they believed pot was safer than alcohol, but had concerns about habitual use and its impact on memory, "making it and education a bad combination," Aidan said.
And they have reason to worry.
Scientists are increasingly concerned about the effects of marijuana on the developing brain, which is not fully mature until about age 25. Some studies show cognitive impairments when the brain is exposed to the drug in adolescence, according to the National Institute on Drug Abuse.
Health professionals at the University of Denver in Colorado are carefully watching the impact of the Rocky Mountain high and pot's potential for dependence.
"It's something we are tuned in to and when we see changes in the rates, like this, we are alerted," said Sarah Belstock, director of health promotion at the college's Health and Counseling Center.
Legal sales and regulation "remove some of the risk," she told NBC News. But college officials have noted a correlation between student GPAs and marijuana use.
"When partying overtakes other areas of life, we often see an academic impact," she said.
Belstock concedes that marijuana use has a "lesser impact" on the university community than alcohol and binge drinking, which continue to reign large on campus.
"You don't see the property damage and violence and general disruptions," she said. "But the individual impact [of marijuana] is a different story."
There may be a silver lining: Campus use of dangerous amphetamines and prescription narcotics is down.
"It appears that college students, at least, are hearing and heeding the warnings about the very considerable dangers of using narcotic drugs," said study author Johnston.
"The marijuana story overshadows a lot of the other drugs," he said. "But I don't think it's as dangerous in the sense that it leads to death like other drugs. It's more subtle."