Addiction is influenced by biological, psychological, and social factors. Biologically, repeated drug use can cause changes in the brain's reward system and stress response. This involves the dopamine system and brain regions like the nucleus accumbens and prefrontal cortex. Withdrawal activates the brain's stress systems and impairs inhibitory control. Genetics may influence the risk of addiction through gene-environment interactions. Adolescence is a risk period due to the brain's ongoing development.