Robert Patterson, the acting administrator of the Drug Enforcement Administration, will retire at the end of the month, a spokeswoman for the federal agency, Mary Brandenberger, told CNN on Monday.
The Washington Post first reported the news that Patterson will step down.
Patterson told agency staff in an email Monday that his work as acting administrator had become "increasingly challenging," according to the Post.
Patterson wrote that "the administrator of the DEA needs to decide and address priorities for years into the future -- something which has become increasingly challenging in an acting capacity," the Post reported.
Patterson was tapped to serve as acting DEA chief in October after the previous acting administrator, Chuck Rosenberg, stepped down. A law enforcement official told CNN at the time that Rosenberg did not want to work in the Trump administration any longer.
Rosenberg had sent his employees an email in July that rebuked President Donald Trump after he told law enforcement officers in New York to be more "rough" with suspects during a speech meant to focus on efforts to combat the brutal gang MS-13.
The Post noted that it is not yet clear who will take over as acting DEA administrator following Patterson's departure.
Patterson wrote in his message to employees that he "tried my best to keep the agency moving forward," according to the newspaper.
"Since taking on the role of acting administrator, I have known that a permanent replacement would eventually be named," he wrote. "As such, I took each day as a gift, and with that mentality tried my best to keep the agency moving forward."