Embattled Rep. Trey Radel (R-Fla.) resigned from Congress Monday, months after pleading guilty to a misdemeanor drug charge.

A first-term congressman, Radel was arrested for cocaine possession in the fall . After reaching a plea agreement, he underwent substance abuse rehabilitation treatment and returned to Congress earlier this month. Despite calls from state party leaders for him to step down, Radel had said he was committed to returning to work.

But on Monday, he swiftly changed course and said he would step down later in the day. In a letter to House Speaker John Boehner (R-Ohio), Radel said his personal struggles impeded his ability to serve in Congress. He said last year that struggles with alcoholism led him to make an "extremely irresponsible choice" involving cocaine.

"Unfortunately, some of my struggles had serious consequences," Radel said. "While I have dealt with those issues on a personal level, it is my belief that professionally I cannot fully and effectively serve as a United States Representative to the place I call home, Southwest Florida."

Radel said his resignation would be effective as of 6:30 p.m. Monday. He also wrote to Gov. Rick Scott (R) and Secretary of State Ken Detzner (R) to inform them of his decision.

Scott will set the date for the special election to fill Radel's seat.

Radel comes from a heavily conservative district where Mitt Romney won more than six out of 10 votes in 2012. His exit is expected to trigger a competitive GOP primary contest. A former TV news reporter, Radel won 30 percent of the primary vote in a crowded 2012 field.

Former state Rep. Paige Kreegel (R), who won about 18 percent of the vote in the 2012 primary, already filed papers to run. Other possibilities include state Senate Majority Leader Lizbeth Benacquisto (R) and former congressman Connie Mack (R).

The 19th district runs from Fort Myers down to Naples.

You can read Radel's letters of resignation below.

Originally posted at 8:46 a.m. This post has been updated.