Ten students and two visitors were hospitalized Sunday from complications arising from the use of the drug Molly or from alcohol.
The Middletown, Connecticut, Police Department reported that 11 were hospitalized because of Molly and one because of alcohol.
The arrested students were Andrew Olson, 20; Rama Agha Al Kakib, 20; Eric Lonergan, 21, and Zachary Kramer, 21, police said in a statement.
They face charges ranging from possession of a controlled substance and possession of a hallucinogen to possession of drug paraphernalia.
Lonergan faces 16 counts of illegally obtaining or supplying drugs.
Wesleyan University has suspended the students.
University President Michael S. Roth has described Molly as a refined form of MDMA with "extremely dangerous" effects. MDMA is the active ingredient in the drug ecstasy.
According to the Drug Enforcement Administration, most often Molly is not MDMA, but a toxic mixture of lab-created chemicals.
And Middletown police said on Tuesday that they expect multiple designer drugs were in the Molly. They have executed four search warrants to find out more about where the drugs came from.
Most of the chemicals are meant to stimulate the central nervous system to cause euphoric highs.
They can also cause a rapid heartbeat, high blood pressure, blood vessel constriction and sweating, and can prevent the body from regulating temperature. Some of the chemicals have been reported to cause intense, prolonged panic attacks, psychosis and seizures.
Roth told all students to stay away from all drugs. "One mistake can change your life forever," he said.