Addiction occurs when repeated use of drugs changes how a person’s brain functions over time. The transition from voluntary to compulsive drug use reflects changes in the brain’s natural inhibition and reward centers that keep a person from exerting control over the impulse to use drugs even when there are negative consequences—the defining characteristic of addiction.
Some people are more vulnerable to this process than others, due to a range of possible risk factors. Stressful early life experiences such as being abused or suffering other forms of trauma are one important risk factor. Adolescents with a history of physical and/or sexual abuse are more likely to be diagnosed with substance use disorders.30 Many other risk factors, including genetic vulnerability, prenatal exposure to alcohol or other drugs, lack of parental supervision or monitoring, and association with drug-using peers also play an important role.31
At the same time, a wide range of genetic and environmental influences that promote strong psychosocial development and resilience may work to balance or counteract risk factors, making it ultimately hard to predict which individuals will develop substance use disorders and which won’t.