Firefighter-paramedics responded at 11:15 p.m. to a report of a man down on Columbus Avenue near Broadway. They arrived to find multiple patients, one of whom was described as belligerent by police.
First responders at the location administered Narcan, a medication that is used to help stabilize a person who has overdosed.
Four men were transported to a hospital, where three were admitted, a spokesperson for the Glendale Police Department said.
Officers were seen wearing full hazmat gear as they entered the home to conduct a search.
Detective Cecelia Cleveland of the Los Angeles Interagency Metropolitan Police Apprehension Crime Task Force, or L.A. IMPACT, later confirmed that drugs were found that tested positive for fentanyl.
Investigators characterized the investigation as isolated, adding that there was no danger to the public.