Maté defines addiction scientifically as the recurring use of a substance despite undesired consequences. He warns against defining addiction too simplistically, because it has so many facets. Then he makes the distinction between compulsive and addictive behaviors. An addiction begins in the pursuit of pleasure. But compulsive urges are unpleasant: Someone who acts compulsively does so in order to make the feeling of abstinence stop.

In his definition of dependence, “The addict comes to depend on the substance or behavior in order to make himself feel momentarily calmer or more excited or less dissatisfied with his life” (139).

Maté addresses the misconception that using a drug will always lead to addiction. Addiction is a human problem not easily reduced solely to chemicals. Exposure does not create risk. A person who becomes an addict is already at risk when encountering the drug.

His primary example is that of soldiers who used heroin during the Vietnam War. When they returned from Vietnam, the remission rate was “95 percent, unheard of among narcotics addicts treated in the U.S.” (142).

Based on animal experiments, and in particular an experiment with rats an addiction known as Rat Park, Maté believes that the roots of addiction are environmental.