The term comorbidity refers to the co-occurrence of two or more diseases, illness or health problems which is nothing but the coexistence of mental health and drug and alcohol disorders. It refers to problems that a person can experience over a lifetime. It’s not just chronic and severe disorders and it is not just an issue for mental health, but also the chronic physical health problems. It has emerged as a major clinical, public health and research issue over the past few decades. The most prevalent problematic drugs for comorbidity are tobacco, alcohol, cannabis, and prescription drugs.
Common mental health comorbidities are personality disorders and mood disorders, such as depression, anxiety, schizophrenia and substance abuse and addiction. Generally disorders may be primary, secondary or independent to each other. Gender is also a factor in the specific patterns of observed comorbidities. Similarly, persons diagnosed with drug disorders are likely to suffer twice from mood and anxiety disorders.
The common factors involved are overlapping genetic vulnerabilities, involvement of related brain regions, overlapping environmental triggers, drug use disorders and other mental illnesses are developmental disorders. Major depressive disorder frequently coexists with other conditions such as post-traumatic stress disorder, substance abuse disorders, and severe physical illnesses or disabilities. Anxiety disorders are often comorbid with schizophrenia, bipolar disorder, post-traumatic stress, and substance abuse. Schizophrenia is frequently comorbid with depression, anxiety, substance abuse and other addictions.
The types are trans-syndromal comorbidity and trans-nosological comorbidity. Trans-syndromal comorbidity is a coexistence in a single patient with two or more syndromes that are pathogentically related to each other, but the division of comorbidity types are mainly preliminary and inaccurate.
The methods of evaluation are done by Cumulative Illness Rating Scale (CIRS), cumulative Illness Rating Scale for Geriatrics (CIRS-G), The Kaplan-Feinstein Index, Charlson Index, modified Charlson Index, Elixhauser Index, Index of Co-Existent Disease, Geriatric Index comorbidity (GIC), Functional Comorbidity Index (FCI) and Total Illness Burden Index (TIBI).
The factors which are responsible for the development of comorbidity can be chronic infections, inflammations, involution and systematic metabolic changes, iatrogenesis, social status, ecology and genetic susceptibility.