Comorbidity is a term that doctors use to describe the simultaneous presence of two or more diseases or disorders within the same person. In addition to merely being present at the same time, these conditions interact significantly, alter each other's expression within the body, and alter each other's long-term outcome. Strong comorbidity exists between substance abuse and mental illness, and fully 60 percent of people who abuse drugs and\/or alcohol also have some form of psychiatric disorder. Particular conditions found in association with drugs or alcohol include depressive disorders and anxiety disorders. The behavioral disorder called attention deficit hyperactivity disorder (ADHD) may lead to substance abuse when it appears comorbidly with one or two other behavioral disorders. Reasons for Comorbidity The comorbidity between substance abuse and mental illness can arise in three basic ways. In some cases, the presence of some form of substance abuse triggers the onset of a specific psychiatric disorder. In other cases, the presence of a specific psychiatric disorder leads to the onset of some form of substance abuse. Apart from these situations, both substance abuse and mental illness can arise together from a common group of underlying influences or circumstances. Common Underlying Factors The National Institute on Drug Abuse lists a variety of underlying factors that can potentially lead to both substance abuse and serious mental health issues. First, both substance abuse and certain psychiatric problems occur, in part, because of changes in pathways inside the brain that process feelings of pleasure, as well as changes in brain pathways that respond to the effects of stress. Second, certain genetically inherited traits may predispose an individual toward both mental illness and substance abuse or, alternatively, make one of these problems more likely to occur if the other one develops. Another potential source of substance abuse\/mental illness comorbidity is exposure to environmental factors such as sexual abuse, physical abuse, other forms of serious stress or trauma, or exposure to drug use early in life. In some circumstances, shared environmental factors may also heighten the effects of shared genetic factors. In addition to these factors, both mental illness and substance abuse commonly begin early in life when childhood or teen growth and development are still active. In these circumstances, the early effects of drug abuse can make mental illness more likely; conversely the presence of mental illness at this stage in life can increase the chances for the onset of substance abuse. Substance Abuse and Depressive Disorders Depressive disorders are sometimes referred to generically as depression. Specific types of these disorders include major depressive disorder, dysthymic disorder, mild depression, and manic-depressive disorder (bipolar disorder). Certain forms of substance abuse tend to appear simultaneously with these disorders, Medscape Education explains. For instance, comorbidity between alcoholism and the various depressive illnesses ranges anywhere from roughly 15 to 70 percent, while comorbidity between cocaine abuse and these illnesses ranges from approximately 33 to 53 percent. Substance Abuse and Anxiety Disorders Common anxiety disorders include generalized anxiety disorder, post-traumatic stress disorder (PTSD), panic disorder, obsessive-compulsive disorder (OCD), and social anxiety disorder (social phobia). Types of these disorders that occur comorbidly with some form of substance abuse include PTSD and social anxiety disorder. In treatment programs for substance abuse across the US, roughly 20 to 45 percent of all participants have symptoms of PTSD, and these people often have relatively poor recovery outcomes for both issues. Roughly 10 to 15 percent of all substance abusers have symptoms of clinical social anxiety. Substance Abuse and ADHD Children and teens with ADHD have significantly, but not dramatically, higher risks for future substance abuse problems than children and teens without the disorder. However, when ADHD occurs comorbidly with a behavioral disorder called conduct disorder, rates for adult substance abuse rise almost three times when compared to rates for people without ADHD or conduct disorder. Similarly, when ADHD occurs comorbidly with another behavioral disorder called oppositional defiant disorder (ODD), rates for future substance abuse rise more than two times when compared to rates for people without ADHD or ODD. Considerations When attempting to identify comorbidities between substance abuse and mental illness, doctors and researchers must make sure that other outside influences are not actually responsible for the problems they find. For instance, some of the symptoms of clinical depression can closely resemble some of the symptoms of drug withdrawal or alcohol withdrawal. If they're not careful, doctors and researchers can mistake withdrawal for depression, misdiagnose the presence of mental illness and falsely identify comorbidity with substance abuse. However, despite these concerns, the links between substance abuse and mental illness are clear. The disorders listed here represent only some of the comorbid conditions found in people who abuse drugs and\/or alcohol.