Citing its policy, the medical examiner's office refused this week to publicly name the drug or drugs responsible for the death of the student, André Narcisse, or say whether the drugs were over-the-counter, prescription or illegal.
At the time, a Yale spokesman said there was no evidence of foul play.
"We again wish to offer our deepest sympathy to André's family and friends," the spokesman, Tom Conroy, said Friday in a statement. "The Yale community will continue to mourn his tragic passing and remember his selfless contributions to the life of the campus."
Narcisse's parents, Jasmine and Jean-Pierre, did not return phone calls Friday seeking comment.
Told of the toxicology results, Alex Katz, one of Narcisse's Exeter classmates, said: "Regardless of the cause of death, it's a tremendous loss."
The day of Narcisse's death, roommates found Narcisse unresponsive in the suite at about 11 a.m., officials said. Medics called to the scene tried unsuccessfully to revive him.
The death shook the Yale campus, which had been the center of national and international media attention following the September slaying of Yale student Annie Le, who also had ties to Long Island. Her body was found hidden behind a lab wall on the day she was supposed to marry a Huntington man in Syosset.
A lab technician, Raymond Clark III, has pleaded not guilty in her murder and is awaiting trial.