The 55-year-old comedian had been sober for 20 years, Buxbaum said.
Williams "found himself drinking again and has decided to take proactive measures to deal with this for his own well-being and the well-being of his family," she said in a statement. "He looks forward to returning to work this fall to support his upcoming film releases."
Buxbaum declined to elaborate beyond the statement.
Williams currently stars in the psychological thriller "The Night Listener," a film based on the best-selling novel by Armistead Marpin. He plays a radio talk show host who develops a telephone relationship with a young listener.
Later this year, Williams will star in "Man of the Year," and serve as the voice of an animated penguin in "Happy Feet," slated for release in November.
He won an Oscar for his supporting role in 1997's "Good Will Hunting."