Sometimes mental health disorders and substance use disorders simply occur independently of one another, and they happen to occur at the same time. However, in many instances, the disorders are tied together and one disorder may lead to another, or be exacerbated by another.
For example, an individual who suffers from depression may turn to alcohol to alleviate the symptoms. However, once the alcohol leaves the body, depression symptoms will return and they may be worsened. The individual may therefore find themselves drinking alcohol more and more regularly in an attempt to manage the symptoms of depression, which could result in alcohol addiction or abuse.
Similarly, substance abuse might cause mental health problems. This might be because drugs or alcohol can generate anxiety or depression, or it may be because some drugs can trigger mental illness in those who are already genetically predisposed to it.
Often, both mental illness and substance abuse can be worsened by circumstances influenced by the mental disorder or substance use. For example, drug abuse could cause loss of employment, financial difficulties, and problems with family and relationships, and these difficulties can all contribute to mental health problems, particularly depression or anxiety. Co-occurring disorders are therefore often cyclical and influenced by a range of factors.