The D.C. Department of Health is investigating six nurses after drugs disappeared at Sibley Memorial Hospital.

The Health Department began investigating in June and is aware of six cases as of last week.

Two nurses’ licenses immediately were suspended.

One of the nurses is accused of possessing hydromorphone, diazepam and lorazepam without valid prescriptions and was fired after refusing to take a drug test. She previously resigned from Walter Reed National Military Medical Center under similar accusations, according to the Health Department.

At a meeting with a Health Department investigator in July, she said she has prescriptions for fentanyl and morphine to treat chronic leg pain and Lyme disease and claimed she was being treated for addiction, but she failed to provide evidence of the prescriptions or the treatment, the Health Department said.

The other nurse is accused of possessing Dilaudid, lorazepam and Percocet without valid prescriptions.

The Health Department charged both with "prescribing, dispensing or administering drugs" without authorization.

Four nurses are under investigation to determine if the drugs are missing due to a mistake or because someone stole them.

"Sibley Memorial Hospital has a zero tolerance policy for any inappropriate use of controlled substances by hospital employees," a statement from Sibley spokesman Gary Stephenson said. "While we are not at liberty to discuss personnel issues, we can assure you any such inappropriate use of controlled substances would be addressed quickly and aggressively, because the safety and well-being of our patients are always our top priority."

The Board of Nursing and Sibley Hospital are assisting the Health Department investigation.