What Is Comorbidity?

When a Person Has More Than One Condition

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.

Comorbidity also describes how the two illnesses interact with each other. In other words, does one illness cause the symptoms of the other to worsen? Another factor that is described by the term comorbidity is how each condition impacts the course and prognosis (outcome) of both diseases.

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

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

Types of Comorbidity

There are many different types of comorbidity, 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). Some types of comorbidity commonly occur together.

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 triglycerides
  • 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 and acid reflux) 
  • An increase in hormone levels, secreted by adipose (fat) tissue, which impacts the endocrine system, this can result in diabetes and other metabolic conditions


It’s very common for people with arthritis to have other chronic (long-term) conditions (comorbidity). According to the Centers for Disease Control and Prevention (CDC) a little over 22% of adults in the United States have arthritis, but arthritis is more common in those with other chronic conditions.

In 2013 through 2015, the prevalence of arthritis in adults with other long-term conditions (comorbidity rate) was:

  • 31% for those with obesity
  • 47% for those with diabetes
  • 49% for those with heart disease


There are a few specific comorbidities commonly linked with diabetes. It’s important not to confuse comorbidities with symptoms. For example, diabetes may make it more difficult to control your blood pressure; therefore, high blood pressure (hypertension) may be a symptom of diabetes.

But, high blood pressure readings, along with diabetes would not be considered comorbidity unless a person meets the specific qualifications (criteria) required for a formal diagnosis of hypertension.

According to the 2020 clinical practice guidelines for hypertension, a person is diagnosed with hypertension when their blood pressure is 140/90 mmHg or higher, following repeated examination. In order to have a comorbidity diagnosis of diabetes and hypertension, each medical condition must be diagnosable on its own.

Other common conditions (comorbidities) associated with diabetes include:

Mental Illness

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)

Keep in mind that a substance use disorder (which includes alcohol or drug abuse and alcohol or drug dependence) is considered a type of mental illness.


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.

People with SPMI often live in residential facilities that provide for their housing and other needs because they are often unable to hold down regular jobs or procure stable housing. They may also need support and collaboration of care for a variety of services such as vocational skills, legal support, parenting and childcare skills, and more.

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.

Was this page helpful?
Article 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. National Institute on Drug Abuse. Comorbidity: Addiction and other mental illnesses. Updated September 2010.

  2. 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

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

  4. 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

  5. Centers for Disease Control and Prevention (CDC). Comorbidities. Updated May 17, 2019.

  6. Unger T, Borghi C, Charchar F, Khan NA, Poulter NR, Prabhakaran D, Ramirez A, Schlaich M, Stergiou GS, Tomaszewski M, Wainford RD, Williams B, Schutte AE. 2020 International Society of Hypertension Global hypertension practice guidelines. Hypertension. 2020;75(6):1334-1357. doi:10.1161/HYPERTENSIONAHA.120.15026

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

  8. 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.

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

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

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

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

  13. 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.

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