“The inability to stop is the essence of what addiction is,” says Nora Volkow, director of the National Institute of Drug Abuse, part of the National Institutes of Health.

That’s not to say that people who can’t make it through the day without latte grandes or Ghirardelli chocolate are addicts, says Volkow, a self-professed “chocoholic” who has pioneered brain-imaging studies of addiction. Caffeine does activate some of the same brain circuits as the drugs of addiction, but only very mildly, she says. Caffeine can be habit-forming, but Starbucks devotees won’t risk jail time or divorce to feed their habit.

Nor is addiction the same as dependence, although the American Psychiatric Association’s diagnostic manual says it is, says Volkow, who’s pushing to drop that wording. “Addiction is much harder to treat. Everybody given an opiate (such as morphine) will become physically dependent, but not everybody will become an addict.”

But some do. Why?

For many, alcohol or other drugs offer a quick fix, Koob says. “You’re using the drug to fix something that should be fixed by perhaps getting a good night’s sleep or pacing yourself.” But the drug eventually wears off, leaving the user feeling even worse than before, and the cycle begins anew, Koob says.

If you want to know whether a child will turn to alcohol or other drugs for a quick fix, look at his parents, says Mark Willenbring, director of treatment and recovery research at the National Institute on Alcohol Abuse and Alcoholism.

If the parents are abusing drugs, chances are high that the child will too, Willenbring says. Having only one or no parent in the home or a psychiatric illness also raises a child’s risk of addiction, he says.

Clearly, addicts are born and made, their genes and their environment inextricably linked, says NIAAA director Ting-Kai Li. Even people genetically predisposed to becoming addicted won’t unless exposed to alcohol or illicit drugs.

“Children who drink early in their childhood are four times more likely to become alcoholics” than those who don’t, Li says. One reason: Their main source of alcohol is the well-stocked fridge or liquor cabinet of parents who drink.

Scientists have known for decades that separating young laboratory animals from their parents made them much more likely to take alcohol. Such studies “didn’t have the impact they should have had, because we didn’t understand why,” Volkow says.

Molecular biology is beginning to provide answers. A rodent study published this year found that contact between offspring and parent is necessary to activate a gene involved in the animal’s response to stress, Volkow says. Environmental stressors in childhood, such as abuse, probably have a longer-lasting effect than similar stressors in adulthood, Volkow says.

Thanks to imaging studies, “we have come to realize that the brain is changing significantly during childhood and adolescence,” she says. Li says the frontal lobe may not fully mature until age 25.

Research has shown that stress is a major contributor to addiction. People who repeatedly take drugs may end up with an exaggerated response to stress, so minor stressors become major ones, says Frank Vocci, director of NIDA’s Division of Pharmacotherapies and Medical Consequences of Drug Abuse.

And even after an alcoholic has stopped drinking or a drug addict has stopped using cocaine, Vocci says, “stress is thought to be a major inducer of relapse.”