Causes
Almost all substances associated with substance use problems affect the "reward mechanism" in the brain. The main chemical messenger involved in the brain's reward mechanism is dopamine. Each time the person uses a substance they feel good, which makes them want to use the substance again. Over time, changes in the brain occur (e.g., less dopamine is produced), which lessens the pleasurable effects of the substance and larger amounts are needed to get the same feeling.
The causes of substance use problems aren't clear, although there are many factors that are thought to play a role. Heredity (genetics) appears to be involved as the risk of substance use problems is higher for people with family members with these problems. A person's environment, such as school, work, friends, family, and cultural and religious beliefs, can also affect substance use problems.
Other mental health conditions such as anxiety and depression may also play a role. Substance use may also start when people try to manage unpleasant feelings and emotions (e.g., anger, stress, sadness). People who are subject to discrimination may also be at risk for substance use problems.