U.S. Rep. Trey Radel said Wednesday night he will take a leave of absence for an unspecified time and donate his salary.
"I have no excuse for what I have done. I have let down our country," he said at a news conference.
Radel spoke to reporters after returning home to southwest Florida, hours after he pleaded guilty to misdemeanor cocaine possession.
The 37-year-old first-term Republican from Florida said he will enter an inpatient drug treatment program to get treatment for substance abuse.
He hopes to set an example for those who struggle with addiction, CNN's Alina Machado reports.
The cocaine possession charge came after authorities said he bought a small amount of cocaine in a sting in the nation's capital last month
During the brief news conference, Radel said he "grew up with a mom who struggled with alcoholism."
"I don't want my son to struggle with that," he said.
The plea and sentence were part of a deal that Radel's attorney struck with federal prosecutors. He could have received a maximum sentence of 180 days imprisonment or a $1,000 fine, or both. Instead, he was placed on one year probation, and if it is "successfully completed," his guilty plea will be cleared from his record.
A throng of rescue workers scoured the coastal Florida waters early Wedenesday morning looking for two people missing from an air ambulance crash. CNN's John Zarrella has the latest.
Authorities have already found the bodies of two others in the Atlantic Ocean, a U.S. Coast Guard spokesman said. The four passengers - two pilots, a doctor and a nurse - had just dropped off a patient at Fort Lauderdale-Hollywood International Airport and was headed back to Mexico, airport spokesman Greg Meyer said.
By early Wednesday, the debris field and search area for survivors had stretched to 20 square miles of the Atlantic, the Coast Guard said.
A distress call from one of the pilots came just moments after takeoff. An air traffic controller asked him to turn left and keep a certain altitude.
"Not possible," the pilot responded.
The pilot asked to turn around. Seconds later, he said: "Mayday, mayday, mayday."
Coast Guard Petty Officer Mark Barney said the bodies of a man and woman were located just off the coast of Fort Lauderdale.
The two medical staff members worked for Air Evac International, said Albert Carson, the company's director of operations. The pilots worked for a chartered company. Carson said it was not immediately clear who was killed and who was still missing.