The addicted brain is distinctly different from the nonaddicted brain, as manifested by changes in brain metabolic activity, receptor availability, gene expression, and responsiveness to environmental cues

There are many biological factors that are involved with the addicted brain. "The addicted brain is distinctly different from the nonaddicted brain, as manifested by changes in brain metabolic activity, receptor availability, gene expression, and responsiveness to environmental cues" (2) In the brain, there are many changes that take place when drugs enter a person's blood stream. The pathway in the brain that the drugs take is first to the ventral tegmentum to the nucleus accumbens, and the drugs also go to the limbic system and the orbitofrontal cortex, which is called the mesolimbic reward system. The activation of this reward system seems to be the common element in what hooks drug users on drugs (2).

Drugs seem to cause surges in dopamine neurotransmitters and other pleasure brain messengers. However, the brain quickly adapts and these circuits desensitize, which allows for withdrawal symptoms to occur (3). Drug addiction works on some of the same neurobiological mechanisms that aid in learning and memories (3). "This new view of dopamine as an aid to learning rather than a pleasure mediator may help explain why many addictive drugs, which unleash massive surges of the neurotransmitter in the brain, can drive continued use without producing pleasure-as when cocaine addicts continue to take hits long after the euphoric effects of the drug have worn off or when smokers smoke after cigarettes become distasteful." (4)

Since memory and pleasure zones are intertwined in the brain, many researchers have been using psychological approaches to stop drug use. Many rehabilitation centers have used classical conditioning to rehabilitate drug addicts. They combine exposure to drugs combined with cognitive scripts, like statements how drugs have destroyed a person's life or what can be accomplished without using drugs, according to DeLetis (5). By using classical conditioning, the drugs addicts pair the drugs with negative connotations and properties. "Adverse withdrawal symptoms can function as an instrumental negative reinforcer and can be linked to the opponent process theory of motivation." (6) However, drug addicts may relapse and start using again because of many environmental "cues", which are external forces that are associated with drug use in their lives. When the drugs addicts see these cues, their brain circuitry, especially the orbitofrontal cortex become hyperactive and causes these people to start craving drugs again (2). No matter how successful the rehabilitation treatment is, once those "cues" are around, the drug addicts remember how pleasurable the drugs felt and relapse into drug abuse again.

Through all of the research done about drug addiction and its affects on the brain, one can see how drug addiction is considered a brain disease. Drug addiction is a disabling disease and can ruin a person's life. By taking drugs, a person's brain becomes "rewired" to tolerate high amounts of dopamine neurotransmitters, but once those high amounts of dopamine cease to exist, the person experiences withdrawal symptoms. However, there are ways drug addicts can control their drug intake by using classical conditioning techniques, which allows them to associate drugs with negative attributes.