An addiction is a chronic dysfunction of the brain's reward system that causes a compulsive pursuit of a substance or behavior despite negative consequences. There are two main types of addiction - physical or chemical addictions which involve substances like alcohol, opioids, cocaine, and marijuana, and behavioral addictions which involve compulsive behaviors like gambling, sex, internet use, and gaming that activate the brain's reward system. Behavioral addictions cause people to lose control over their actions in order to engage in brief pleasurable behaviors.