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A. The Biology Behind Drug Addiction

Narrator: This is Science Today. Evidence that drug addiction has a biological basis is being studied at the University of California, San Francisco. Dr. Robert Malenka, a professor of psychiatry, says drug addiction is now viewed by many scientists as a biological brain disorder, similar to depression.

Malenka: Obviously, it's not just biology. There's incredibly important environmental influences, individual psychological differences that contribute to whether somebody becomes addicted or not, I mean those influences are clearly incredibly important.

Narrator: But Malenka says so are biological influences. Clinical studies have found drugs of abuse can activate neural circuits in the brain responsible for a natural reward process.

Malenka: A natural reward is associated with feelings of warmth - filling up your stomach when you eat food. The thought is that a drug of abuse sort of goes in there, interacts with these neural circuits and activates them, but in an unnatural way.

Narrator: Chronic intake of drugs seems to alter the natural reward process permanently. For Science Today, I'm Larissa Branin.