Substance abuse refers to the harmful or hazardous use of psychoactive substances, such as alcohol or drugs, which can lead to negative consequences such as physical, social, or mental health problems. Addiction, on the other hand, is a complex brain disease characterized by compulsive drug seeking and use despite harmful consequences. While substance abuse may lead to addiction, not everyone who abuses drugs or alcohol becomes addicted. Addiction involves changes in the brain that make it difficult to quit or control substance use, and typically requires specialized treatment and support to manage.