Substance addiction does not only refer to dependence on substances such as heroin or cocaine. A person who cannot stop taking a particular drug or chemical has a substance dependence. Addiction is a psychological and physical inability to stop consuming a chemical, drug, activity, or substance, even though it is causing psychological and physical harm. When a person experiences addiction, they cannot control how they use a substance or partake in an activity, and they become dependent on it to cope with daily life.