Certain personality disorders also raise the odds of drug abuse and alcohol abuse. Narcissistic patients, who constantly battle feelings of inadequacy, are frequently drawn to stimulants, like cocaine, that provide a fleeting sense of power and self-confidence. People with borderline personality disorder, who struggle to control their impulses and anger, often resort to drugs and alcohol to soften their intolerable moods.

But precarious mental health is not the only risk for long-term addiction. Emerging evidence suggests that drug abuse can be a developmental brain disorder, and that people who become addicted are wired differently from those who do not.

Dr. Nora Volkow, director of the National Institute on Drug Abuse, has shown in several brain-imaging studies that people addicted to such drugs as cocaine, heroin and alcohol have fewer dopamine receptors in the brain’s reward pathways than nonaddicts. Dopamine is a neurotransmitter critical to the experience of pleasure and desire, and sends a signal to the brain: Pay attention, this is important.

When Dr. Volkow compared the responses of addicts and normal controls with an infusion of a stimulant, she discovered that controls with high numbers of D2 receptors, a subtype of dopamine receptors, found it aversive, while addicts with low receptor levels found it pleasurable.

This finding and others like it suggest that drug addicts may have blunted reward systems in the brain, and that for them everyday pleasures don’t come close to the powerful reward of drugs. There is some intriguing evidence that there is an increase in D2 receptors in addicts who abstain from drugs, though we don’t yet know if they fully normalize with time.

But people are not brains in a jar; we are heavily influenced by our environments, too. The world in which Ms. Winehouse traveled appears to have been awash in illicit drugs and alcohol whose use was not just accepted but encouraged. Even people who aren’t wired for addiction can become dependent on drugs and alcohol if they are constantly exposed to them, studies have found.

Drug use changes the brain. Primates that aren’t predisposed to addiction will become compulsive users of cocaine as the number of D2 receptors declines in their brains, Dr. Volkow noted. And one way to produce such a decline, she has found, is to place the animals in stressful social situations.