A new book challenges the ingrained idea that there are 2 'types' of addiction, and it could change everything we know about drugs and alcohol

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To be truly addicted to a drug, the conventional wisdom goes, you have to be psychologically and physically hooked.

In other words, you have to both crave the drug and feel physically sick — for example, shaky or nauseated — when you can't get it.

But is this necessarily true?

In her new book, "Unbroken Brain," science writer Maia Szalavitz argues that the line between these two seemingly separate aspects of addiction is much fuzzier than most of us think.

And keeping up the distinction, while it might seem intuitively appealing, is doing more harm than good. Here's why:

Our bodies and brains react differently to different types of drugs

First of all, our physical and psychological reactions to drugs aren't universal across drug types. We don't respond to depressants like alcohol and heroin the same way we respond to stimulants like cocaine and meth.

When we regularly use a depressant like alcohol, for example, two things tend to happen in our bodies and minds:

1. We develop a physical tolerance for it, meaning that each time we drink, we need more to achieve the same warm, pleasant feelings.
2. We experience physical withdrawal when we suddenly stop drinking: We feel nauseated, shaky, or physically ill in other ways. We may also experience psychological withdrawal, meaning we crave or strongly desire to drink again.

Conversely, when we regularly use a stimulant like cocaine, very different things can happen to us physically and psychologically:

1. We either develop partial tolerance or sensitization: In partial tolerance, we need slightly more of the drug each time to experience the same high. In sensitization, smaller amounts of the drug actually cause more intense effects. This virtually opposite reaction can happen in some regular users.
2. We tend to go through psychological — but not physical — withdrawal when we suddenly stop using, meaning we might crave or strongly desire to use the drugs again, but not using them won't make us physically ill. "Stimulant withdrawal doesn't make you physically ill like heroin or alcohol withdrawal does; nearly all of its signs can be dismissed as 'psychological' rather than 'physical' and include things like irritability, craving, depression, and sleep disturbances," Szalavitz writes.

It's tough to put the signs of addiction into two distinct mind or body categories — and this gets at a bigger problem with the way we view and treat addiction.

For one thing, focusing on whether a drug's effects are primarily psychological or physical tends to obscure how dangerous it may be. In the 1970s and '80s, for example, many scientists regarded cocaine as fairly harmless because it didn't produce obvious symptoms of physical withdrawal like shaking or vomiting.

In a 1982 article in Scientific American, for example, renowned University of California at San Francisco psychiatrist Craig Van Dyke and infamous Yale psychopharmacologist Robert Byck compared the behavior of people who'd used cocaine to that of people who'd recently indulged in a delicious snack. The behavioral pattern of users, they wrote, was "comparable to that experienced by many people with peanuts or potato chips. It may interfere with other activities ... but it may be a source of enjoyment as well."

This sort of thinking would have drastic consequences. The number of people who admitted using cocaine on a routine basis jumped from 4.2 million in 1985 to 5.8 million in 1989, according to data from the Drug Enforcement Administration. During that same four-year period, cocaine-related hospital emergency room visits increased 28-fold.

"The lack of physical signs of dependence like vomiting and diarrhea in stimulant addiction made scientists see stimulant problems as less severe," writes Szalavitz. "You might want cocaine or speed, the thinking went, but you didn't need it like a real heroin junkie."

Just because someone isn't vomiting when they aren't using doesn't mean they're not addicted

To say that drugs that don't produce obvious symptoms of physical withdrawal — vomiting, diarrhea, etc. — makes them somehow "less addictive" is dangerous, naive, and above all else, unscientific, writes Szalavitz. At the end of the day, "both kinds of symptoms ultimately [are] expressed via chemical or structural changes in the brain." Whether these symptoms are visible in our bodies or felt in our minds, then, matters far less than what effects they ultimately produce in the brain.

And these effects are key to understanding how people get addicted to a substance — whether it's heroin, cocaine, marijuana, nicotine, or methamphetamine.

"While withdrawal from marijuana, cocaine ... and numerous other drugs does not result in the stereotypical 'opiate-withdrawal-flu-like-syndrome,' there is no doubt that real withdrawal from these substances exists for long term users," writes University of California at Los Angeles psychiatrist Adi Jaffe in a blog post for Psychology Today. "Fatigue, depression, anxiety, sleep disturbances, and trouble eating are only some of the symptoms that tend to show up."

We need to keep this in mind if we can ever hope to properly diagnose, treat, or prevent addiction.

"As far as I'm concerned, if you have a behavior that is making your life miserable and which you can't seem to stop, it doesn't matter if you're throwing up during withdrawal or not," writes Jaffe. "It's an issue and you need help."

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