By BENEDICT CAREYFEB. 10, 2014

The life of a heroin addict is not the same as it was 20 years ago, and the biggest reason is what some doctors call “heroin lite”: prescription opiates. These medications are more available than ever, and reliably whet an appetite that, once formed, never entirely fades.

Details are still emerging about the last days ofPhilip Seymour Hoffman, the actor who died last week at 46 of an apparent heroin overdose. Yet Mr. Hoffman’s case, despite its uncertainties, highlights some new truths about addiction and several long-known risks for overdose.

The actor, who quit heroin more than 20 years ago, reportedly struggled to break a prescription painkiller habit last year. Experts in addiction say that the use of medications like Vicodin, OxyContin and Oxycodone — all opiates like heroin — has altered the landscape of addiction and relapse, in ways that affect both current users and former ones.

“The old-school user, pre-1990s, mostly used just heroin, and if there was none around, went through withdrawal,” said Stephen E. Lankenau, a sociologist at Drexel University who has surveyed young addicts. Today, he said, “users switch back and forth, to pills then back to heroin when it’s available, and back again. The two have become integrated.”

Rates of prescription opiate abuse have risen steadily over the last decade, while the number of people reporting that they used heroin in the past 12 months has nearly doubled since 2007 to 620,000, according to government statistics. That’s no coincidence, researchers argue: more people than ever now get a taste of opiates at a young age, and recovering addicts live in a world with far more temptations than there were a generation ago.

“You can get the pills from so many sources,” said Traci Rieckmann, an addiction researcher at Oregon Health & Science University. “There’s no paraphernalia, no smell. It’s the perfect drug, for many people.”

Millions of people use these drugs safely, and doctors generally prescribe them conscientiously. But for some patients, prescription painkillers can act as an introduction — or a reintroduction — to an opiate high. The pills set off heroin craving in recovering addicts, doctors say, every bit as well as they soothe withdrawal in current users.

Dr. Jason Jerry, an addiction specialist at the Cleveland Clinic’s Alcohol and Drug Recovery Center, estimates that half of the 200 or so heroin addicts the clinic sees every month started on prescription opiates.

“Often it’s a legitimate prescription, but next thing they know, they’re obtaining the pills illicitly,” Dr. Jerry said.

In many parts of the country, heroin is much cheaper than prescription opiates. “So people eventually say, ‘Why am I paying $1 per milligram for oxy when for a tenth of the price I can get an equivalent dose of heroin?’ ” Dr. Jerry said.

Investigators do not yet know whether Mr. Hoffman was taking prescription opiates at the time of his death. Toxicology tests are pending, and the purity and content of the heroin found in his apartment will certainly be a focus.

While the deluge of prescription painkillers is new, other risk factors for overdose have not changed in decades.

Post-rehab — after having gotten clean — addicts are vulnerable to overdose because they misjudge their tolerance level, which has dropped. Pre-rehab, many addicts will binge one last time, also inviting trouble.

“These are common danger zones,” said Dr. Nicholas L. Gideonse, the medical director of O.H.S.U. Richmond Community Health Center in Portland.

Even a change in where a person uses his or her drug of choice can increase the likelihood of an overdose, studies suggest. “If you habitually use in your car, for example, the body prepares itself to receive the drug when it’s in that environment,” Dr. Rieckmann said. “It’s called conditioned tolerance. When people using are in an unfamiliar places, the body is less physically prepared.”

The risk of dying from an overdose is higher when people are using alone. “Another person, sober or not, can notice when someone nods off, or just say, ‘Hey man, slow down,’ ” Dr. Lankenau said. “And users act as a gauge for each other of when they’re doing something dangerous.”

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Many needle exchange programs and clinics now have overdose prevention courses, teaching users to notice danger signs and administer the drug naloxone, an opiate blocker that E.M.T.s use to revive addicts who have overdosed.

None of which might have spared Mr. Hoffman. One thing that has not changed for heroin addicts over the past 20 years is the certainty that this next shot will not be deadly.

“You have to understand that addicts inject three or four times a day for years and years on end,” Dr. Gideonse said. “They don’t perceive any one shot to be dangerous or potentially deadly, because in their experience, there’s no reason to.”