In the past, Limbaugh has decried drug use and abuse on his bluntly conservative show, mocking President Bill Clinton for not inhaling and often making the case that drug crimes deserve punishment.
"Drug use, some might say, is destroying this country. And we have laws against selling drugs, pushing drugs, using drugs, importing drugs. ... And so if people are violating the law by doing drugs, they ought to be accused and they ought to be convicted and they ought to be sent up," Limbaugh said on his short-lived television show on Oct. 5, 1995.
During the same show, he commented that the statistics that show blacks go to prison more often than whites for the same drug offenses only illustrate that "too many whites are getting away with drug use."
Law enforcement sources who spoke on condition of anonymity confirmed to The Associated Press that Limbaugh was being investigated for by the Palm Beach County, Fla., state attorney's office.
"Immediately following this broadcast, I am checking myself into a treatment center for the next 30 days to once and for all break the hold this highly addictive medication has on me," he said Friday.
"You know I have always tried to be honest with you and open about my life," Limbaugh said. "So I need to tell you today that part of what you have heard and read is correct. I am addicted to prescription pain medication."
Attempts to reach Limbaugh by phone, e-mail, fax and at his Florida home were unsuccessful Friday.
Limbaugh gave up his job as an ESPN sports analyst Oct. 1, three days after saying on the sports network's "Sunday NFL Countdown" that Philadelphia Eagles quarterback Donovan McNabb was overrated because the media wanted to see a black quarterback succeed.
The reports of possible drug abuse surfaced at about the same time, first in the National Enquirer. The tabloid had interviewed Wilma Cline, who said she became Limbaugh's drug connection after working as his maid. She said Limbaugh had abused OxyContin and other painkillers.
Mike Edmondson, a spokesman for the Palm Beach County state attorney's office, said Friday his office could neither confirm nor deny that an investigation was under way. Limbaugh's attorney, Roy Black, did not return a message seeking comment.
CBS News Correspondent Paul Moniz reports experts tell him addiction to these types of drugs is difficult to treat long-term. Studies of abstinence rates show that only 30-50 percent of rehab patients are able to remain drgu-free at one year and, at 12 years, only 25 percent are drug free.
"Some specialists regard prescription drug addiction as a chronic disorder and say a realistic treatment goal is sharp reduction in use, not total abstinence, Moniz says.
This is Limbaugh's third time in rehab, Moniz adds.
Limbaugh said he started taking painkillers "some years ago" after a doctor prescribed them following a spinal surgery. His back pain stemming from the surgery persisted, so Limbaugh said he started taking pills and became hooked.
"Over the past several years I have tried to break my dependence on pain pills and, in fact, twice checked myself into medical facilities in an attempt to do so. I have recently agreed with my physician about the next steps."
A spokesman for Premiere Radio Networks, which syndicates the politically focused "Rush Limbaugh Show" to more than 650 markets, declined to elaborate on Limbaugh's previous treatment.
OxyContin is a narcotic painkiller that is widely prescribed for victims of moderate to severe chronic pain resulting from such problems as arthritis, back trouble and cancer.
Limbaugh reported two years ago that he had lost most of his hearing because of an autoimmune inner-ear disease. He had surgery to have an electronic device placed in his skull to restore his hearing.
Research has found that abuse of opiate-based painkillers like OxyContin can lead to profound hearing loss caused by damage to the inner ear, said Dr. Gail Ishiyama, an assistant professor at the UCLA department of neurology. She could not confirm that was Limbaugh's case without access to his medical history.
Steve Plamann, executive editor of The National Enquirer, said he was gratified by Limbaugh's admission and his plans to seek help.
"We didn't do our stories gleefully. We just reported the facts," Plamann said.
However, Limbaugh said that reports about his addiction have inaccuracies and distortions which he will clarify when he is able to speak about them.
Premiere spokesman Michael Sitrick said Limbaugh is expected to return to his program after completing treatment. Several guest hosts were scheduled until then.