The percentage of teens who think there is a great risk from being a regular marijuana user has dropped, according to a new survey. The Monitoring the Future survey found 39.5 percent of 12th graders think regular marijuana use is harmful, down from 44.1 percent last year.

Monitoring the Future is an annual survey that measures drug use and attitudes among students in grades 8, 10 and 12. The survey found 6.5 percent of high school seniors smoke marijuana daily, compared with 6 percent in 2003, and 2.4 percent in 1993, CNN reports.

“This is not just an issue of increased daily use,” National Institute on Drug Abuse Director Nora D. Volkow, MD said in a news release. “It is important to remember that over the past two decades, levels of THC – the main psychoactive ingredient in marijuana – have gone up a great deal, from 3.75 percent in 1995 to an average of 15 percent in today’s marijuana cigarettes. Daily use today can have stronger effects on a developing teen brain than it did 10 or 20 years ago.”

Almost 23 percent of seniors say they smoked marijuana in the month prior to the survey, and just over 36 percent say they smoked it during the past year.

The survey found use of synthetic marijuana, also known as K2 or Spice, decreased 3.4 percent among high school seniors. Less than 1 percent of all students surveyed said they used bath salts. “Synthetic drugs are particularly dangerous because their ingredients are unknown, they have not been tested for safety and their ever-changing ingredients can be unusually powerful,” said lead researcher Lloyd Johnston. “Users really don’t know what they are getting.”

The abuse of the painkiller Vicodin has decreased in the last 10 years, from 10.5 percent of high school seniors in 2003, to 5.3 percent this year. The survey also found 7.4 percent of seniors said they took the ADHD drug Adderall for non-medical purposes in the past year, while 2.3 percent reported abusing Ritalin.