Kindai University said Monday at least five of its 58-member soccer club had used cannabis, and the case was reported to police.
The university in Osaka Prefecture said it will set up a team to investigate all of its roughly 33,000 students over illegal drug use.
It said the case, which the police are investigating on suspicion of violating the Cannabis Control Law, came to light on Wednesday after a member of the male soccer club talked about the matter with a coach.
During a club meeting the following day, the five admitted to using cannabis, with one of them later saying during questioning that he did it "out of interest and because of boredom due to the new coronavirus (pandemic)," according to the institution.
One of the five, who is in his third academic year, bought cannabis for between ¥7-8,000 ($66-$76) per gram from a dealer he contacted via Twitter and used it five or six times at his home between last December and May, the university said.
Three others have used it once or twice at his home between last November and May, while the remaining member used it last October after getting cannabis from a person he met at a nightclub in the city of Osaka and used it on the street, the university said.
At a news conference, university vice president Hisao Atsumi said the five men have not been arrested, but they will be penalized in line with its rules after the investigation ends.
The university on Thursday ordered the soccer club, founded in 1972, to suspend its all activities indefinitely.