Cannabis use among US college students has reached a 30-year high, according to a new Monitoring the Future study from the University of Michigan.

It surveyed more than a thousand Americans aged 19-22 and found that 38% had used cannabis in the past year and 21% in the past month. That is the highest level seen since 1987, and it represents a huge increase over the past decade.

“The continued increase of daily marijuana use among noncollege youth is especially worrisome,” said John Schulenberg, principal investigator of the Monitoring the Future Panel Study.

“The brain is still growing in the early 20s, and the scientific evidence indicates that heavy marijuana use can be detrimental to cognitive functioning and mental health. Getting a foothold on the roles and responsibilities of adulthood may be all the more difficult for these one-in-eight non-college youth who use marijuana on a daily or near daily basis. As for college students, we know from our research and that of others that heavy marijuana use is associated with poor academic performance and dropping out of college.”

The team speculated that cannabis use is rising due to the perception of risk of harm dwindling, particularly as it is legal in some states and used to treat medical conditions. Just 27% of the youngsters surveyed said that they perceive there is a risk of harm associated with regular marijuana use.

Cannabis is even more popular with high school graduates that do not go to college, as 41% of them said they had smoked weed in the past year. Vaping is becoming increasingly popular and 14% of non-college youth said that they had vaped cannabis in the past year, as did 11% of college students.

The researchers found no increase in usage of drugs like cocaine, MDMA, amphetamines and LSD. They said that the likes of ketamine, heroin, crack and crystal meth never gained a foothold on American campuses. Drinking rates are declining year on year among American youth, while tobacco use is dwindling massively.

“The findings regarding tobacco use continue to be an important part of the good news from our study,” said Schulenberg. “The new record lows in cigarette smoking among college students, combined with declines in the use of other forms of tobacco suggests that today’s college students have been given the context and tools to increasingly avoid tobacco use, a benefit that will accrue with age.”