Almost 6 percent of college students say they use marijuana daily or almost daily, the highest rate since 1980, a new study finds.

That rate is up from 3.5 percent in 2007. In 1980, 7.2 percent of college students said they smoked marijuana every day or almost every day, Reuters reports. The findings come from the University of Michigan’s Monitoring the Future study.

“It’s clear that for the past seven or eight years there has been an increase in marijuana use among the nation’s college students,” study author Lloyd Johnston said in a news release. “And this largely parallels an increase we have been seeing among high school seniors.”

The researchers said looser marijuana policies in some states likely have contributed to an increase in use by teens and young adults. They are more likely than in past years to perceive the drug as harmless. Last year, 35 percent of high school graduates ages 19 to 22 said they thought regular marijuana use was dangerous, compared with 55 percent in 2006.

An estimated 41 percent of college students used any illicit drug in 2014, compared with 34 percent in 2006. Much of the increase was due to marijuana use, the study found. Use of some illicit drugs, such as synthetic marijuana, among college students has decreased in recent years, while use of heroin and LSD has remained low.

Stimulants and Ecstasy continue to be popular among college students, but their rate of use is leveling out or declining, the article notes. Cocaine use is increasing, from 2.7 percent in 2013 to 4.4 percent in 2014.