An off-duty Buffalo, NY, police officer overdosed on heroin last week, but was revived when an on-duty city police officer responded to a South Buffalo residence and administered at least two doses of the opiate antidote Narcan, three police sources said, reports the Buffalo News .

The Northeast District officer, 26, was revived and taken to Mercy Hospital, two of the sources said. He later requested and was granted an unpaid medical release and is under investigation by the department's Internal Affairs Division.

The incident has shaken members of the police force, who have been responding to hundreds of opiate overdose calls over the past two years. Since the beginning of 2014, more than 350 people have died from overdoses across Erie County, including 23 in an 11-day period from Jan. 29 to Feb. 8, according to the county Health Department. And the epidemic has shown no signs of abating.

"The department has a zero-tolerance policy on drugs, and something like this really is shocking. Right now, we are in shock mode. This is unheard of," said one officer.

Officers who discussed the overdose expressed disappointment that one of their own would take heroin.

"This is the first time we have had an officer who had taken heroin," one of three police officers said. "We've had other officers in the past who have lost their jobs because they tested positive for marijuana or cocaine, but this is the first time we've had heroin."

The department normally conducts random drug testing on officers once a year, but that has not happened for more than two years after a contract concluded with a medical review officer, according to Police Benevolent Association President Kevin Kennedy.

"The city is hoping to have a new medical review officer in place by April or May and the plan is to have 100% testing every year for four years," Kennedy said.