Denver ? Two of seven University of Colorado students hospitalized in one night last month for alcohol poisoning had a “date rape” drug in their system, Boulder police say.

The women were sickened on Sept. 24. Investigators have determined that most drank alcohol at one or both parties at the Sigma Pi and Phi Kappa Tau fraternity houses, police said.

It was unclear whether police had determined whether the women who had the doses of gamma hydroxybutyrate (GHB), a rapidly acting central nervous system depressant, were at the fraternities.

One of the women had a potentially fatal amount of the drug, police spokeswoman Julie Brooks said.

“We do not believe at this point that they voluntarily ingested GHB,” Brooks said.

Further blood tests were being done, although Brooks did not know on how many of the women.

“This is a frightening situation, to think that someone is spiking the drinks of women with a dangerous drug at these parties,” Police Chief Mark Beckner said in a statement.

CU’s fraternities have been in turmoil since a 18-year-old freshman pledge, Lynn Gordon “Gordie” Bailey Jr., died on Sept. 17, 2004, after a night of heavy drinking during a fraternity event.

After Bailey’s death, the university gave the Greek system several stipulations to be recognized as an official student group, including delaying freshman rush until the spring semester. The fraternities refused, deciding instead to operate independently from CU.

Marc Stine, Greek advocate for the fraternities, said police were still investigating and he hoped people would refrain from jumping to conclusions until that work was completed.

“We don’t know where else they may have had alcohol or where else they may have been slipped GHB,” Stine said.

He said all fraternity members have been told to cooperate with police, and “heads will roll” if they are found to be involved.

“Whoever did it, we need to find out and they need to be punished,” Stine said.

Last month, CU’s Interfraternity Council decided that chapters would be able to have parties only at outside venues with liquor licenses.

Stine also said the Sigma Pi and Phi Kappa Tau’s national fraternities were discussing what actions, if any, they would take against the local chapters. They could choose to move forward on the alcohol incidents before the investigation into the GHB is complete.