Research has found that about half of individuals who experience a substance use disorder (SUD) during their lives will also experience a co-occurring mental disorder and vice versa. Co-occurring disorders can include anxiety disorders, depression, attention-deficit hyperactivity disorder (ADHD), bipolar disorder, personality disorders, and schizophrenia, among others.
While SUDs and other mental disorders commonly co-occur, that does not mean that one caused the other. Research suggests three possibilities that could explain why SUDs and other mental disorders may occur together:
- Common risk factors can contribute to both SUDs and other mental disorders. Both SUDs and other mental disorders can run in families, suggesting that certain genes may be a risk factor. Environmental factors, such as stress or trauma, can cause genetic changes that are passed down through generations and may contribute to the development of a mental disorder or a substance use disorder.
- Mental disorders can contribute to substance use and SUDs. Studies found that people with a mental disorder, such as anxiety, depression, or post-traumatic stress disorder (PTSD), may use drugs or alcohol as a form of self-medication. However, although some drugs may temporarily help with some symptoms of mental disorders, they may make the symptoms worse over time. Additionally, brain changes in people with mental disorders may enhance the rewarding effects of substances, making it more likely they will continue to use the substance.
- Substance use and SUDs can contribute to the development of other mental disorders. Substance use may trigger changes in brain structure and function that make a person more likely to develop a mental disorder.