"I have had a problem with alcohol. I have decided to take action by checking myself into an intensive recovery program," the 57-year-old broadcast journalist said in a written statement.
"Overcoming this problem is a top priority in my life and I am excited to return to work as soon as I am able," he continued.
There were no details about the recovery facility or when O'Brien entered the program.
O'Brien, who covered the Summer Olympics in Greece for MSNBC and NBC late-night programming, was a TV news reporter in Los Angeles and Chicago before joining CBS Sports.
He occasionally hosted "Entertainment Tonight" and in 1997 became the full-time host of "Access Hollywood." That contract expired last year and he began hosting "The Insider."
"We support Pat's decision to seek treatment and look forward to welcoming him back on the air at the appropriate time," said Manfred Westphal, a spokesman for Paramount Domestic Television, which syndicates "The Insider."
Westphal said the show's New York host, Lara Spencer, will take over during O'Brien's absence.