Addiction: Addiction is possible whenever ingesting a substance causes the basic pleasure and reward circuits in the brain to activate. Addiction is an illness that requires treatment, because people with addictions cannot stop on their own. Symptoms of addiction include a person's inability to stop using the substance, devoting a lot of time and effort toward obtaining, using, and recovering from the substance's effects, discontinuing important social, employment, and recreational activities due to preoccupation with the substance, developing tolerance for the substance, and developing withdrawal symptoms.