Substance dependence is a medical condition characterized by an individual's compulsive use of a substance, despite harmful consequences. This condition often leads to tolerance, where a person needs to consume more of the substance to achieve the same effect, and withdrawal symptoms when they try to stop. Common substances involved include alcohol, nicotine, and various drugs. People with substance dependence may prioritize their substance use over important activities and relationships. Treatment often involves therapy, support groups, and sometimes medication to help manage cravings and withdrawal symptoms. Early intervention can improve outcomes and support recovery.