1.) Did heroin kill actor Philip Seymour Hoffman?

Officially, the cause of Hoffman’s death is still under investigation: an autopsy on his body was scheduled for Monday in New York. But there appears to be strong evidence that heroin played a role.

Law enforcement sources have said that Hoffman, 46, was found in the bathroom of his New York apartment with a needle still stuck in his arm. On Monday, CNN cited unnamed law enforcement sources as saying that Hoffman’s apartment was littered with signs of a serious heroin habit. The network reported that investigators found close to 50 bags containing what is believed to be heroin in his apartment. In addition, CNN said, investigators also found several bottles of prescription drugs in Hoffman’s apartment, and more than 20 used syringes in a plastic cup.

2.) Did Hoffman have a known drug problem?

He told interviewers that he had a serious problem in his youth--which, apparently had returned in the last few years. “I got sober when I was 22 years old” and went into a drug rehabilitation program at the time, Hoffman told CBS’s “60 Minutes” in 2006. Asked whether he abused drugs or alcohol, Hoffman said: “It was all that stuff. Yeah. It was anything I could get my hands on. Yeah. I liked it all.”

Hoffman had said he stayed clean for two decades, but then had a relapse in 2012, and entered a drug-treatment program.

3.) So how prevalent is heroin use, nationwide?

It’s still lower than the use of other illegal drugs, which is good news. But the bad news is that the number of heroin users now appears to be rising fast. In 2012, for instance, a federal survey found that 23 million Americans had used at least one drug in the previous month. Of those people, 18.9 million had used marijuana, 1.6 million had used cocaine, and 1.1 million had used hallucinogens. By contrast, about 335,000 had used heroin the last month, the survey showed.

But that number was nearly double what it was in 2007.

“It’s a concern--it’s a public health concern--when you see drug use going up like this, but in the context, it’s still a small percentage of the people who use drugs,” said Peter Delany, a top official at the federal Substance Abuse and Mental Health Services Administration.

4.) What’s the reason for that increase?

Delany said officials are still trying to figure that out: one reason might be that there is purer heroin on the market, often available for lower prices. Another possible reason: a crackdown on the abuse of prescription painkillers like OxyContin. Police have targeted the doctors who have prescribed them, and drug companies have altered the pills to make them harder to crush and snort.

As a result, police have said, users have switched to heroin--which can be cheaper, per dose, than prescription pills. In fact, one recent study found that about 80 percent of people who tried heroin for the first time had previously used prescription drugs. That kind of new user has been blamed for increases in heroin in rural areas from northern New England to rural Kentucky, places where there was an existing problem with prescription-drug abuse.

The problem is that these new users are now buying a street drug, instead of one originally made by a drug company. For street buyers, the potency and purity of a heroin dose are usually impossible to know.

“If you go to heroin, you don’t know who you’re getting it from, what it’s cut with, what quantity can I handle,” Capt. Nancy Demme of the Montgomery County police’s Special Investigations Division told the Washington Post recently. “The results are that you have these overdoses and, in some cases, you have deaths.”

5.) How does heroin work?

Basically, by targeting receptors built into the brain and designed to receive a class of natural chemicals: endorphins. Heroin is derived from the poppy plant, like morphine, and both work in basically the same way.

A summary by PBS’s “FRONTLINE” explained it this way:

“Although they seem to be triggered by stress, endorphins can do more than relieve pain, they actually make us feel good. Like an evil twin, the morphine molecule locks onto the endorphin-receptor sites on nerve endings in the brain and begins the succession of events that leads to euphoria.”

Typically, a heroin user experiences a short but powerful “rush” just after taking the drug, and then a high that lasts four to five hours. “It is described as a warm, drowsy, cozy state. Addicts report a profound sense of satisfaction, as though all needs were fulfilled,” the “FRONTLINE” summary says. “There is also a pleasant state of mild dizziness that is not as impairing as alcohol’s effects, and a sense of ‘distancing’ or apathy toward whatever is going on in the environment.”

6.) How does heroin kill you?

One way is by overdose. In those cases, the problem is often that heroin shuts down the natural reflex that causes the body to breathe.

In other cases, the problem is that a heroin user unknowingly takes a dose that includes other drugs. In the last few months, states around the East Coast have reported major problems with doses spiked with acetyl fentanyl, a powerful drug usually given as a last-resort painkiller to seriously ill people.

The Drug Enforcement Administration has reported an overall increase in overdose deaths from heroin in recent years. The annual total rose from 1,879 in 2004 to 3,038 in 2010--the most recent year for which the DEA provided data.

In some cases, the victims of these overdoses have been young people, trying the drug for the first time. That was the case with Emylee Lonczak, a 16 year-old student at McLean High School in Virginia who died in August, after being injected with the drug by a friend. She fell unconscious, and friends dragged her outside and left her. Her body was found two days later.

7.) What is known about the heroin Hoffman had with him?

Its “stamp names,” the drug world’s equivalent of a trademark. The drugs that Hoffman had with him bore the names Ace of Spades and Ace of Hearts. The New York Post reported that police are searching New York for the dealers who sold Hoffman his drugs. If his death was indeed caused by drugs, investigators may need toxicology tests to determine what the dose was made up of.

8.) Someone close to me has a problem with heroin. What can I do to get help?

The government’s Substance Abuse and Mental Health Services Administration has a Web site that lays out options for people seeking drug treatment. Find it here: http://www.samhsa.gov/treatment/.

The agency also operates a 24-hour Treatment Referral Routing Service. The number is 1-1-800-662-HELP.