“I don’t feel like drugs are much of a problem on this campus,” said Damaris Giha, 18, a freshman. “I feel like alcohol is more of a problem. It’s not something I hear a lot about.”

An older student said drug use was not uncommon. “It’s college, so it’s the kind of place where you see a lot of drugs,” said Lew Bibler, 20, a junior. “People here are smart and they’re trying to get through college, so I see how it could happen.”

The fraternities are not as central to the social scene as they are at some other colleges, he added.

Aliya Zlotkin, 21, is not a student at Columbia but said she was a friend of Adam Klein, one of the defendants. “He’s a great guy; he’s a really exceptional person,” said Ms. Zlotkin, who described him as smart and kind, a focused student majoring in biology studies. “This just came absolutely out of the blue for him.”

Columbia’s director of media relations, Robert Hornsby, declined to comment when asked if the university was taking any disciplinary action against the students.

The university did issue a statement to students, which said, in part: “The alleged behavior of the students involved in this incident goes against not only state and federal law, but also university policy and the principles we have set  and strive together to maintain  for our community. Please rest assured we are taking this matter very seriously.” The university said drug counseling and treatment were available for students.

Three people who the police said had been the students’ suppliers were also arrested on drug charges: Miron Sarzynski and Megan Asper, whom the authorities described as his girlfriend, were arrested on Oct. 27 in Mr. Sarzynski’s East Village apartment; and Roberto Lagares was arrested on Sunday in Bedford-Stuyvesant. Mr. Sarzynski also faces kidnapping charges; the authorities said he tried to hire an undercover officer to abduct a rival drug dealer at gunpoint in retaliation for a $4,000 debt. Mr. Sarzynski proposed holding his rival for ransom and torturing him by feeding him LSD.