All but one of the patients had been released by late Saturday afternoon, said Scott Ferguson, chief of the Cle Elum-Roslyn-South Cle Elum Police Department.
Eleven of the overdose or poisoning victims were women.
The last remaining patient had been in critical condition at Kittitas Valley Community Hospital, but her status was later upgraded, Ferguson said.
He said it was disturbing that people at the party didnt call authorities to report there were unconscious victims there.
I hate to think what could have happened had we waited longer, he said, calling the incident absolutely unprecedented in the Roslyn area.
CWU President James Gaudino said the university would begin a lengthy process to sanction any students who were involved.
Its certainly our sense that this is an isolated event, he said.
Despite the size of the party about 50 people were said to be present neighbors apparently saw and heard nothing that caused them to call the authorities .
The partygoers were mainly underage CWU students and their friends. The party occurred at a weekend home belonging to the parents of a CWU student, Ferguson said.
That student has been cooperating with the investigation, the chief added.
Ferguson said investigators suspect that someone spiked drinks that were intended for the young women in attendance. The symptoms described are typical of a date rape drug, but Ferguson said an extensive search of the home did not uncover any drug evidence.
Police said they were investigating a possible rape involving a couple at the party, but they said they could not confirm that there was a widespread plan to sexually assault the intoxicated women.
A Kittitas County sheriffs deputy reported seeing a man performing a sex act on his semiconscious girlfriend. The man was not arrested, but the incident remains under investigation because of the womans possible inability to consent.