Substance abuse can cause depression in several ways. One possible explanation is that drug or alcohol use can alter the brain’s chemistry and disrupt the balance of certain chemicals, including serotonin, dopamine, and norepinephrine, which are responsible for regulating mood. Substance abuse can also lead to changes in sleep patterns, energy levels, and appetite, which can contribute to feelings of depression. Additionally, substance abuse can lead to problems in relationships, work, and other areas of life, which can increase stress and feelings of hopelessness. Finally, withdrawal from drugs or alcohol can also cause symptoms of depression, which can make it more difficult to quit using. It is important to seek professional help if you are struggling with substance abuse and depression.