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Last week we looked at the science of pleasure… the biochemistry of the brain’s reward system. This week, what happens when that mechanism goes wrong. Addiction.

How can something that’s start off being pleasurable end up making us feel so low?

Mike Williams talks to scientists and former addicts in the search for some answers.

Produced by Ben Carter

(Photo: Collection of different hard drugs Heroin, Pills, Tobacco and Alcohol. Credit to Shutterstock)