The seven male inmates at Halawa Correctional Facility who were hospitalized Thursday morning were treated for “drug intoxication,” according to the state Department of Public Safety.

At around 11:40 a.m. on Thursday, Honolulu Emergency Medical Services responded to a 911 call from the facility, which reported that there were prisoners who needed emergency medical care for unknown illnesses.

It’s still unclear what type of drugs were used and why they made the inmates sick. DPS spokeswoman Toni Schwartz told the Honolulu Star-Advertiser in an email Friday that “drug intoxication” was a hospital diagnosis, but couldn’t say if the inmates overdosed or if the drugs they used were contaminated.

She added that the department cannot release more information about the hospitalizations due to an active investigation. The Honolulu Police Department and the DPS Narcotics Enforcement Division have been notified, and an internal and law enforcement investigations are underway.

It also has yet to be revealed how the inmates obtained the drugs, although Schwartz said that contraband is “an ongoing battle for correctional facilities across the nation.”

“Stopping contraband from entering any correctional institution is a continuous effort that we prioritize to ensure the health, safety and welfare of our staff, the community, as well as the inmates,” she said in a statement. “We are committed to fighting this battle, by rooting out the pathways, curbing contraband introduction in our facilities and working with our federal, state and county law enforcement and prosecutorial partners to bring those who violate this law to justice.”

The seven hospitalized inmates were returned to HCF by 6:40 p.m. on Thursday.

In a statement attributed to Scott Harrington, the correctional facility’s warden, he said, “I want to personally thank my hard-working staff for their quick response. They noticed something was wrong and went into immediate action to assess the inmate’s health and put out the call for medical assistance all while maintaining constant security control.”