The college years in the United States are a time for students to experiment. Many U.S. colleges and universities urge their students to explore a variety of ideas, interests and even ways of thinking that may be different or new to them.

Most Americans who go to college usually do so right after high school, when they are away from home for the first time. John Schulenberg believes that because of this separation from family members, some of the experimentation done on college campuses is not healthy.

Schulenberg is a research professor at the Institute for Social Research at the University of Michigan. He notes that for years, drug and alcohol use by students has been a big issue at U.S. colleges and universities.

Many movies and television shows present drug and alcohol use as just a normal part of the college experience. Yet Schulenberg told VOA that it has a lasting effect on students' overall well-being.

"The fact is the brain is still growing ... through the mid-20s," he said.

That is why Schulenberg is concerned about evidence of increasing use of the drug marijuana at U.S. colleges and universities. In July, he and a team of researchers published a study. It found that in 2018, marijuana use among college-aged Americans reached the highest level since 1983.

The researchers examined the behavior of about 1,500 young people, between the ages of 18 and 22, after their final year of high school. Almost 1,000 of these men and women were admitted to a college or university, while the rest were not. The study found that about 43 percent of those questioned reported using marijuana sometime during the past year. About 25 percent reported using it sometime within the past month.

In this photo taken Monday, February 9, 2015, a display model single-use vaporizer electronic joint, left, is displayed with the packaged marijuana oil concentrate cartridge used with reusable vaporizers at a pot shop in Seattle.

Earlier research has suggested links between heavy marijuana use and poor academic performance and mental health issues. But Schulenberg worries more about another finding of the new study. It shows that the number of people vaping marijuana doubled between 2017 and 2018. They use an electronic device, such as an e-cigarette, to combine water vapor with marijuana. The vapor contains tetrahydrocannabinol, or THC, a chemical found naturally in the cannabis plant.

Schulenberg says he has never before seen any form of drug use double in just one year.

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