"I have had a problem with alcohol," O'Brien said. "I have decided to take action by checking myself into an intensive recovery program. Overcoming this problem is a top priority in my life and I am excited to return to work as soon as I am able."
Co-host Lara Spencer will fill in until O'Brien returns.
Paramount Domestic Television spokesman Manfred Westphal said: "We support Pat's decision to seek treatment and look forward to welcoming him back on the air at the appropriate time."