Now that he has embarked on his third formal attempt to kick an addiction to prescription drugs, conservative radio talk show host Rush Limbaugh is likely to find that getting off narcotic painkillers is the easy part.

The hard part, experts say, will be staying clean.

"The problem is that people want to go into treatment, have that episode be over and then live happily ever after, which is not the way it works," said Wilson Compton, a psychiatrist at the National Institute on Drug Abuse, who spent a decade as medical director of a treatment program.

When it comes to kicking a prescription drug habit, Compton and others say, relapse is the rule rather than the exception. Recovery is a lifelong process that requires an addict to fashion a new life without a pharmacological cushion that exerts profound effects on the brain as well as the psyche.

The painkillers Limbaugh abused, which reportedly include Vicodin and OxyContin, a drug known as "Hillbilly Heroin" because of its popularity in rural southern communities, serve multiple purposes. They create a powerful sense of euphoria and well-being; blur the distinction between fantasy and reality; quell depression and anxiety; and relieve the physical misery that drives many users to take the drugs in the first place.

The drugs, known as opiates, attach to receptors in the brain and spinal cord and block the transmission of pain messages to the brain. Excessive long-term use of opiates appear to alter brain chemistry by overstimulating the brain's reward pathways, reinforcing the desire for greater doses of the drug.

Limbaugh has said he started taking the painkillers, which are chemical cousins of heroin, five or six years ago to treat pain from failed spinal surgery. He said that his two previous attempts at rehab failed.

Experts in drug treatment say that is not unusual: Most addicts relapse at least once, as do most people who try to stop drinking or smoking. Researchers say they do not know how many times it takes to achieve sobriety, because that question has not been well studied in users of drugs other than nicotine. But most agree that overcoming a painkiller habit tends to be more difficult than treating an addiction to alcohol, cocaine or nicotine.

"Treating this kind of addiction is more complex," said Jon Morgenstern, director of the division of treatment research at the National Center on Addiction and Substance Abuse at Columbia University. "There are tremendous cravings initially to go back and use which must be managed to prevent relapse."

While statistics vary widely and there are few studies of prescription drug abusers, about half of heroin addicts who undergo treatment are either dead or on long-term methadone maintenance 30 years later, Morgenstern said. Methadone, a synthethic opiod, is a legal substitute for heroin; it is also used to treat prescription drug addicts.

"We think the incredibly poor recovery rates among heroin addicts may be related to significant changes in their brain chemistry," said Marvin D. Seppala, medical director of Minneapolis-based Hazelden, one of the nation's oldest and best known inpatient substance abuse programs.

While many people start taking narcotic painkillers after surgery or an accident, most of them automatically taper their dose as the pain recedes and then stop taking the drugs altogether. Addicts behave differently, ratcheting up the dose as the pain subsides because they like -- and then crave -- the feelings the drugs induce. Most depend on the medications to manage their moods, not pain.

Cindy McCain, wife of Sen. John McCain (R-Ariz), has said her addiction to Vicodin, which began after she started taking the drug after back surgery, helped her get through the "Keating Five" savings and loan scandal of the 1980s in which her husband was implicated.

"The pills made me feel euphoric and free" even while she was sitting through blistering testimony about her husband in Senate hearings, McCain has written. She said she overcame her addiction years ago.

Hooked on a Pathway

While federal statistics illustrate a dramatic increase in the number of people abusing addictive painkillers, particularly OxyContin, most people who take these drugs never get hooked.

"Addiction is defined by addictive behaviors," Seppala said. These include taking more pills than prescribed, shopping for doctors who will prescribe medication, filling prescriptions at multiple pharmacies, and clandestine or compulsive use of medication. Cindy McCain has described locking herself in the bathroom to gobble five or six pills so no one could see how many she was taking.

Despite the popular notion that there is an "addictive personality," experts dismiss the concept as a myth. Researchers simply do not know why some people can take OxyContin for years to treat severe chronic pain without becoming hooked, while others become addicted in a matter of weeks. The reasons, Morgenstern speculated, probably include a complex mix of poorly understood factors, among them a genetic predisposition to addiction, an inability to handle stress and impulsivity.

"We know that all addictive substances interact with a common reinforcement pathway," said Compton, director of prevention research at NIDA. "We're still trying figure out exactly what the pathways are."

Compton and other experts say that prescription drug addicts face a hurdle not shared by alcoholics or people who take street drugs. Many pill addicts delude themselves into thinking that they don't really have a problem because the drug they are taking is legal and has been prescribed by a physician for a medical problem.

Overcoming that denial is critical, said psychologist John Schwarzlose, president of the Betty Ford Center in Rancho Mirage, Calif., which has treated more than 62,000 people since its founding more than 20 years ago. About 10 percent of these patients, Schwarzlose said, were primarily addicted to painkillers.

"An addict is an addict," Schwarzlose said, adding that this is a view treatment centers try to impress on all patients. "And a person who can still function no matter what they're addicted to is the most difficult to intervene on." Most addicts, he noted, are working and some can function at a high level, as did Limbaugh, who until his recent leave of absence hosted a regular five day a week radio show.

The Usual Treatment

Regardless of the drug of choice -- painkillers, heroin, crack, tranquilizers -- inpatient drug treatment typically follows a similar path: detoxification followed by behavioral therapies, usually group and individual therapy, and faithful attendance at Narcotics Anonymous (NA) meetings.

The self-help group, founded 50 years ago by recovering heroin addicts in Los Angeles, is similar to Alcoholics Anonymous and is predicated on a combination of anonymity, spirituality and personal responsibility. Addicts are encouraged to attend self-help meetings for months or years after they leave treatment for the support and to help prevent relapse.

Withdrawal from opiates is riskier and more unpleasant than detox from alcohol or cocaine, experts say. "With normal alcohol detox, you rarely run into any complications," Schwarzlose said. "But with opiate addiction, even if you use the right medications and the right treatment approach, addicts can go through incredible mental and physical difficulties when they detox."

Detox is similar to a bad case of the flu and can take about a week, he said. Patients typically experience intense feelings of jitteriness and bouts of sleeplessness, which can last much longer.

Earlier this year, the Food and Drug Administration approved a drug called buprenorphine, which blunts the symptoms of withdrawal and the cravings addicts feel. Some treatment centers also administer clonidine, a blood pressure drug, to ease withdrawal.

While some patients who undergo withdrawal from painkillers find that a few weeks after detox the physical misery that initially caused them to take the drugs has vanished, others must confront chronic pain. For these patients, Hazelden and other treatment centers usually try alternatives to narcotics: acupuncture, relaxation techniques including yoga, nonnarcotic painkillers and sometimes surgery. If these fail, officials may consider a tightly controlled treatment with lower doses of opiates.

"The ideal is complete abstinence, but for a small group of patients in rare cases we would set up an extensive program of monitoring and support," Hazelden's Seppala said. One such program involved a recent Hazelden patient who suffered multiple injuries and underwent many surgeries after a devastating motorcycle accident; opiates were the only things that eased his pain. Hazelden helped set up a program that requires he receive treatment from only one physician experienced in both pain management and addiction, and that he get his prescriptions filled at a single pharmacy.

One factor that will inevitably affect Limbaugh after treatment is his celebrity. While fame and wealth may have prolonged his addiction, his future is at stake. And that, they say, may help him, as it has other addicts.

"He's got a tremendous motivation -- his career is on the line," observed Joseph A. Califano Jr., president of the Center on Addiction and Substance Abuse at Columbia University. Califano noted that studies have found that the prospect of job loss, more than other factors such as the threat of divorce or loss of custody, tends to force people to stay clean.

Schwarzlose said that has been the experience at Betty Ford, which has treated more celebrities than most centers.

"Our most successful group of patients are airline pilots," Schwarzlose said. He notes that more than 90 percent of pilots treated at Betty Ford for drug or alcohol abuse do not relapse.

The reason, he said, is this: The Federal Aviation Administration does not give them a second chance. "They're told they can be tested at any time and if their urine is dirty, they'll never fly again," he noted.

Actors and other entertainers, Schwarzlose added, don't fare nearly as well.

"In that world," he said, "there's no incentive."