When my teenage son was raging out of control on drugs — wasted on crystal meth and heroin, careening toward death — I finally got him into treatment, the first of a dozen rehab programs he would go to. This program included lectures for family members, like one titled “The Disease of Addiction.” By then Nic had lied to me, broken into our home, and stolen from me — and even from his little brother, too. I thought I’d raised a kind, moral, and loving child, but something had gone horribly wrong. As I listened to the speaker talk about addiction as a disease, Nic was in a lockdown ward in a wing of the hospital. Getting him there had been hell — he almost leaped out of our moving car and had tried to kick out the window. My son wasn’t ill. He was selfish, reckless, and remorseless, a narcissistic teenager obsessed with being high, with no concern for his family.

That was the first time I heard what is sometimes termed “the disease theory” of addiction, but it wasn’t the last. I tell about my struggle to understand that addiction is a disease in my book Beautiful Boy, about about my family’s struggle when Nic became addicted. The disease theory was repeated in more lectures at more rehabs, in countless therapists’ offices, and in many Twelve Step meetings I attended. I’d become enraged by it. People with leukemia have a disease. Those with Alzheimer’s or lymphoma have a disease. Nic was choosing to use and could stop if he wanted to. There was no such option for cancer patients.

Meanwhile, I struggled to make sense of what had happened to my son.

My perplexity, not to mention my fear, led me to spend the next ten years investigating this thing called addiction. I wanted to confirm my view about espousers of the disease theory, that they were looking for an excuse for addicts’ appalling behavior.

As I report in my latest book, Clean: Overcoming Addiction and Ending America’s Greatest Tragedy, a disease, according to Stedman’s Medical Dictionary, is “an interruption, cessation, or disorder of a body, system, or organ structure or function” and “a morbid entity ordinarily characterized by two or more of the following criteria: recognized etiologic agent(s), identifiable group of signs and symptoms, or consistent anatomic alterations.”

In researchers’ laboratories, I was shown scans of addicts’ brains compared with ones of “normal” brains that showed startling differences in the ways they functioned. Researchers showed how the brains of addicts responded to drugs differently than did nonaddicts’ brains. They explained the consistent anatomic aberrations found in the brain structure of addicts and the disruption they had of the normal flow of neurotransmitters through the nervous system. I was informed about research that demonstrated that addicts’ brains were different even before they took drugs and given incontrovertible evidence of genetic components of addiction.

I also learned about functional differences in addicts’ brains and common symptoms associated with addiction. Over time, addicts’ neurological systems build up a tolerance to a given drug. Because they become physically dependent on the drug, they experience withdrawal symptoms, some potentially lethal, when they’re deprived of the drug. Craving and associated drug-seeking behavior are other typical symptoms. All of these symptoms are caused by biology, not choice. Impairments include a range of cognitive deficits and compromised motor functions. There are measurable anomalies related to autonomic body functions.

Over time I became convinced. The evidence was undeniable. Addiction is a disease, but a unique disease because of the associated behavior. And it’s unique because it appears that people choose it.

People do choose to use drugs — at first. Nic chose to get high, but so do most other children. Before they are eighteen, 80 percent of our kids do. Most of them stop or continue to use in moderation, but some, about one out of ten, become addicted. Like Nic. He was twelve when he smoked pot for the first time. His use quickly escalated, and by the time he was eighteen, he was addicted to it. Nic didn’t choose to become addicted. No one does. Once addicted, sufferers of the disease continue to use in spite of a desire, at some point desperation, to stop. Often they repeatedly try to stop, but they can’t. Addicts’ brains are different than others’. This is a disease that impairs the parts of the brain that would normally cause people to control their impulses.

My son was ill — seriously ill. The disease of addiction is chronic and progressive. If it isn’t treated, it can be fatal. It became clear to me: Nic could die of this disease.

I’ve heard some people say that addiction shouldn’t be considered a disease because a diagnosis would discourage addicts and their families, as if it were a sentence that would doom them. But I was relieved when I understood that Nic was ill. Nic’s unconscionable behavior made sense. I heard addicts describe the need for drugs as as powerful as the need for oxygen. Deprive a person of oxygen, and he will kick, scratch, and fight for more. Deprive an addict of drugs, and he will lie, steal, and do other irrational things — whatever it takes — to get more. The diagnosis was also a relief to Nic, who’d been as mystified as I was by behavior of his that he, too, found inexplicable.

I gathered my research in Clean. The book considers the social, political, biological, health, behavioral, and other aspects, including the consequences, of the disease of addiction. One of my goals for the book was to once and for all prove to skeptics that addiction is a disease. It wasn’t merely an intellectual exercise. I came to understand that people must know that addicts are ill if our society is ever going to solve the myriad problems associated with addiction, which is now the number-three killer in America, costing the nation $425 billion for health care, criminal justice, and lost productivity.

Clean was published in April of this year. I braced myself for attacks about some of the stands I take in the book. I expected some readers and special-interest groups to vehemently disagree with my positions on marijuana legalization and the war on drugs. (I concluded that marijuana, though dangerous for adolescents, should be legalized and that the war on drugs had failed and should be ended.) I expected some drug-treatment professionals to attack conclusions I’d made about, for example, the dangerous constructs of “hitting bottom” and cold-turkey detox (they potentially lead to death and should be rejected) or the usefulness of pharmacology in the treatment of some addictions (contrary to the adamant view of some, you do treat some drug problems with drugs). But those subjects turned out to be far less contentious than my attempt to prove that addiction is a disease.

Recently, my friend Mike Moritz, chairman of Sequoia Capital, wrote an article called “Why Is Addiction Still Considered a Personal Weakness?” tackling the subject. “When we hear about someone with a heart problem, HIV, cancer or diabetes we conclude they are ill,” Mortiz wrote. “If we encounter people whose throats close when they eat peanuts or require epinephrine shots if they mistakenly eat shellfish, we understand there are aspects of their genetic wiring that make them susceptible. Yet when we hear about someone with a drug or alcohol problem, they are all too easily dismissed as weak, self-indulgent, indolent, sinful, narcissistic, debauched and feeble failures. Why don’t we assume that drug and alcohol addicts are ill and often seriously and chronically sick?”

Many people were vitriolic in their responses to both his article and my book. Their vehemence and anger caught me off guard. A man wrote, “I have no sympathy for people who make bad choices, and that’s what addicts do. They’re derelict and must be treated as such.”

“I don’t want my tax dollars or insurance premiums or whatever else wasted on other people’s bad choices,” another responded. “The label of ‘disease’ for drug addictions evokes way too much sympathy from people, and thus is misleading. And it is THAT which I cannot stand.”

Yet another: It’s simple. People make choices in their lives. They make good or bad choices. Their choices are informed by their consciences or lack thereof. Addicts have chosen their own pleasure over everything and everyone. I have no sympathy.”

And more:

“You can make the decision to use drugs or not to. That’s called will power. Some people have no will power.”

“Addiction to substances such as narcotics, alcohol, nicotine, or others is … a choice or lack of will to change.”

“It’s a personal weakness.”

“I’m sick of this ‘oh, poor addicts, they have a disease.’ Addicts just like being high more than they like being sober. They don’t care about the consequences of this choice, which is why they’re reprehensible.”

I realized that if my goal now was to convince people that addiction is a disease, I had my work cut out for me. I learned that I’m taking on deeply rooted prejudices. For some people, the bias is grounded in a belief that if addicts were seen as ill, they’d be off the hook for the choices they made, including reprehensible behavior — violence, or unconscionable actions that break up families and send some addicts to prison. I also determined that the intense reaction comes because people are threatened. They don’t want to accept that sometimes our behavior is not in our control. Our culture emphasizes self-determination and willpower. We want to be the masters of our own destiny.

But sometimes we aren’t.

No matter why people respond to the idea with such vehemence, addiction is a disease — a brain disease.

Why does it matter so much what people think? It matters because we judge and punish people who make bad choices. We demand of them confession and contrition. On the contrary, when people are ill, we treat them with compassion, and the course forward is clearer. People who are ill don’t need blame, chastisement, or punishment — they need treatment.