Philip Seymour Hoffman’s death from a presumed overdose Sunday shocked people who knew about how successful he’d been in battling his addiction issues. Treatment professionals, however, rarely are surprised by news about a relapse.

“You can’t take your sobriety for granted,” said Dr. Marvin Seppala, chief medical officer at Hazelden. “This is a lifelong illness. People have got to stay wary for the rest of their lives.”

It will take an autopsy to determine the official cause of Hoffman’s death, but heroin was found in his New York City apartment, and the friend who found his body told police that there was a syringe still in his arm.

Hoffman, 46, often talked about being addicted to drugs in his early 20s, but said he had kicked the habit and stayed clean and sober for 23 years. Early last year, however, the Oscar-winning actor checked himself into rehab for what was described as a problem with pain pills.

It’s a classic relapse pattern, Seppala said.

“The biggest period for relapses is the first six to 18 months” after rehab, he said. “But then it drops over time, getting easier [to stay sober] the longer you go. You rarely see this situation with people over 20 relapsing.”

Unless something happens — and that something often is taking pain medication.

“We see this scenario regularly,” he said. “There are times when you need to take a pain pill — you had surgery or a broken leg and there just isn’t any other option. If you get other people’s support and you don’t alter the dose and you stop taking them right when the pain is gone, you can safely do it. But it’s still a significant risk.”

There are other things that can trigger a relapse, including a traumatic emotional event or finding oneself in a high-stress situation. It also could be something as simple as hearing a song or meeting an old friend.

“Let’s say you were using a certain drug in a certain place with certain people under certain circumstances,” Seppala said. “For whatever reasons, if you get back into those circumstances, that could be just enough to trigger your subconscious to start moving toward a relapse.”

When someone does relapse after a lengthy sobriety, the results can be dire.

“There’s a lot of shame and guilt,” he said. “They feel, ‘I should know about all this, but here I am using again.’ They have the knowledge of how to get sober again and what to do to stay sober, but they just can’t put it to use for some reason.”

Carol Falkowski, CEO and founder of Drug Abuse Dialogues, said, “Relapse can be triggered by stress or a traumatic event or some life-changing incident — except when it’s not. In other words, it can be something or it can be nothing in particular; it varies by individual.”

Joan Mathews-Larson, executive director of the Health Recovery Center in Minneapolis, doesn’t believe relapses are inevitable, however.

“The best thing that could happen in treatment is to look for underlying causes” of the addiction, she said. “If you’re only going to treat the symptoms, underneath is still that cause doing its mischief.”

It sets in motion a vicious circle of failure, she said. “They never get well, and then they start to feel ashamed. They end up just going from treatment to treatment.”