What Is Comorbidity?

When a Person Has More Than One Condition

Table of Contents
View All
Table of Contents

Comorbidity is the presence of two or more conditions occurring in a person, either at the same time, or successively (one condition that occurs right after the other). Conditions described as comorbidities are often long-term (chronic) conditions.

When two or more illnesses or conditions happen at the same time or successively, it’s also referred to as comorbid. Other names for comorbid conditions include co-occurring conditions, coexisting conditions, and less commonly, multiple chronic conditions, as well as multimorbidity.

According to a study published by the Annals of Family Medicine, "Comorbidity is associated with worse health outcomes, more complex clinical management, and increased healthcare costs."

Mental health and substance abuse support group
SolStock / E+ / Getty Images

Examples of Comorbidities

There are many different possibilities of comorbidities, from coexisting mental illness and drug abuse to co-occurring conditions such as diabetes and high blood pressure. A comorbid condition can include a physical illness and a mental illness (such as cancer and major depressive disorder).

There are many illnesses that tend to co-occur with others for various reasons. It could be that the risk factors are the same for two specific diseases, so a person is more likely to get each of them.

Also, the symptoms of one illness can predispose a person to another. For example, having anxiety often makes a person more prone to self-medicate with drugs or alcohol.

Common Comorbidities

These conditions have commonly occurring comorbidities.


Obesity is known to predispose people to many comorbid illnesses. In fact, there are approximately 236 medical problems (including 13 types of cancer) linked with obesity, according to the Obesity Medicine Association. Common comorbidities for those who are obese include:

  • Insulin resistance: A condition that is considered a precursor to type 2 diabetes
  • Type 2 diabetes
  • Hypertension: High blood pressure
  • Dyslipidemia: High blood lipid levels, such as high cholesterol
  • Cardiovascular disease
  • Stroke
  • Arthritis
  • Sleep apnea: A sleep disorder in which breathing repeatedly stops for short periods of time
  • Gallbladder disease: Such as gallstones or cancer
  • Hyperuricemia: High uric acid levels and gout
  • Osteoarthritis: Degenerative joint disease
  • Certain types of cancer: Such as breast cancer and colorectal cancer, as well as gallbladder cancer
  • Depression

Examples of factors involved in the development of comorbidities for those with obesity include:

  • Physical/metabolic stress which may cause many of the body's organs (such as the heart and kidneys) to become negatively impacted
  •  Biomechanical stress which is caused by the impact of carrying around excess weight, this can result in comorbidities such as osteoarthritis 
  • Biomechanical forces that can cause an increase in weight pushing on the chest and diaphragm, this can cause the soft tissues of the neck to collapse (leading to sleep apnea)
  • An increase in hormones and other substances secreted by adipose (fat) tissue, which impacts the endocrine system, this can result in diabetes and other metabolic conditions


Common conditions (comorbidities) associated with diabetes include:

Psychiatric Comorbidities

According to the Substance Abuse and Mental Health Services Administration’s (SAMHSA) 2018 National Survey on Drug Use and Health, nearly 9.2 million adults in the U.S. have a comorbidity that includes substance abuse and a mental illness or two types of mental illness such as anxiety and depression.

Co-Occurring Disorders

A substance use disorder can involve alcohol or drug addiction (or both). Comorbid substance use disorder and mental illness (also called co-occurring disorders, dual diagnosis, and less frequently referred to as MICD (mental illness/chemical dependency) are common.

When it comes to comorbid substance use disorder and mental illness, the National Institute on Drug Abuse reports that nearly half of those who have one condition—either mental illness or substance abuse—also have the other.

In the 1980s dual diagnosis was initially identified, but as time has gone on, SAMSHA decided to use the term co-occurring disorders (COD) for comorbidities in the mental health field. People with a co-occurring disorder have one or more substance-related disorder along with one or more mental disorder.

Those with a substance use disorder are more likely to have a mental illness and individuals with mental illness are more likely to have substance use disorder. This is not necessarily because the symptoms of each disorder cause a person to have a comorbidity.

Rather, the risk factors are the same for substance abuse and mental health disorders, which predisposes a person with either condition, to have both. Also, some symptoms of substance use disorder can cause people to self-medicate (using drugs or alcohol).

A third factor in why co-occurring disorders are so common when it comes to mental illness is that chronic (long-term) drug or alcohol use can adversely impact the brain, making a person more likely to develop mental illness.

Depression and Anxiety

One of the most common examples of comorbidity in the mental health field is depression and anxiety disorder. According to the National Alliance on Mental Illness (NAMI), some sources estimate that nearly 60% of those with anxiety also have symptoms of depression and visa versa.

Some of the most common mental health disorders in people with substance use disorder include mood and anxiety disorders such as:

Mood disorders:

  • Major depression
  • Dysthymia
  • Bipolar disorder

Anxiety disorders:

  • Post-traumatic stress disorder
  • Panic disorder
  • Social anxiety
  • Generalized anxiety disorder
  • Obsessive-compulsive disorder

Those with conditions considered serious and persistent mental illness (SPMI) are at the highest risk of having co-occurring mental health and substance use disorders. SPMI diagnoses, sometimes referred to as thought disorders, include:

  • Schizophrenia
  • Schizoaffective disorder (a chronic disorder that involves hallucinations, delusions and symptoms of a mood disorder).


The most important thing to keep in mind about treatment, when it comes to comorbidity, is that it often requires consultation and planning between various healthcare providers and organizations. This applies to those with multiple mental health conditions as well as those with physical comorbidities.

After being hospitalized, people with multiple health problems often need assistance and support from organizations such as home healthcare agencies and social services, to address needs such as being unable to work due to a major disability, housing needs, physical care, and more.

When it comes to co-occurring disorders for those with serious and persistent mental illness (SPMI), it’s often a revolving door between treatment facilities, behavioral health hospitalizations, discharge to home, then back into treatment or to a hospital admission again.

A Word From Verywell

Comorbidity involves more than one diagnosis at once, or two or more illnesses which occur back to back. There are many different causes of comorbidity. There may be a chance occurrence that a person has a comorbidity.

Risk factors for certain types of illnesses overlap, and these independent risk factors often impact each condition when a person has a comorbidity. These are referred to as "overlapping risk factors." Another possibility is when one disorder actually causes another.

It's important to keep in mind is that although you may have an illness that is commonly associated with other specific conditions or symptoms (such as high blood pressure), it doesn't necessarily mean that you will be diagnosed with a comorbidity.

Frequently Asked Questions

  • What does comorbidity mean?

    Comorbidity is the presence of two or more medical conditions that exist simultaneously with—and independently of—each other. An example is having diabetes and coronary artery disease.

  • Are comorbidities and complications the same thing?

    With comorbidity, there are two or more co-occurring medical conditions that develop independently of each other, even though there may be shared risk factors. A complication is an adverse event that arises as a direct consequence of a disease, such as diabetic kidney disease in people with type 2 diabetes or AIDS dementia in someone with HIV.

  • What is the Charlson Comorbidities Index?

    The Charlson Comorbidities Index is a system used to predict mortality in people with comorbid conditions in order to determine how aggressively a condition needs to be treated. Each comorbid condition is scored on a scale of 1 (such as for diabetes) to 6 (such as for metastatic cancer) and then added together for the final score.

  • What does comorbidity mean in psychiatry?

    In psychiatry, comorbidity is the presence of one or more diagnoses (such as obsessive-compulsive disorder and an eating disorder). However, because the diagnosis of psychiatric disorders are based on criteria rather than medical tests, comorbidity doesn't always mean that there are multiple diseases but rather that a single diagnosis can't explain all of the symptoms.

Was this page helpful?
14 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Valderas JM, Starfield B, Sibbald B, Salisbury C, Roland M. Defining comorbidity: implications for understanding health and health servicesAnn Fam Med. 2009;7(4):357-363. doi:10.1370/afm.983

  2. Alexander, L. Diseases related to obesity. Obesity Medicine Association. Updated March 13, 2018.

  3. Khaodhiar L, McCowen KC, Blackburn GL. Obesity and its comorbid conditions. Clin Cornerstone. 1999;2(3):17-31. doi:10.1016/s1098-3597(99)90002-9

  4.  National Association of Managed Care Physicians. Co-Morbidities.

  5. Substance Abuse and Mental Health Services Administration. Key substance use and mental health indicators in the United States: Results from the 2018 National Survey on Drug Use and Health. August 2019.

  6. National Institute of Drug Abuse. Comorbidity: Substance use disorder and other mental illnesses DrugFacts. Updated August, 2018.

  7. Hryb K, Kirkhart R, Talbert R. A call for standardized definition of dual diagnosisPsychiatry (Edgmont). 2007;4(9):15-16.

  8. Salcedo B. The comorbidity of anxiety and depression. National Association of Mental Illness (NAMI). Updated January 19, 2019.

  9. Halzelden Publishing. Co-occuring disorders. 2016.

  10. National Institute on Drug Abuse. Common Comorbidities with Substance Use Disorders Research Report. What are the treatments for comorbid substance use disorder and mental health conditions? April 2020.

  11. Klein DN. Different reasons for comorbidity require different solutionsWorld Psychiatry. 2004;3(1):28.

  12. Ording AG, Sorenson HT. Concepts of comorbidities, multiple morbidities, complications, and their clinical epidemiologic analogs. Clin Epidemiol. 2013;5:199-203. doi:10.2147/CLEP.S45305

  13. Roffman CE, Buchanan J, Allison GT. Charlson Comorbidities Index. J Physiother. 2016 Jul;62(3):171. doi:10.1016/j.jphys.2016.05.008

  14. Van Loo HM, Romeijn JW. Psychiatric comorbidity: fact or artifact? Theor Med Bioeth. 2015;36(1):41-60. doi:10.1007/s11017-015-9321-0