Skip to main content

Explainer: What Are Comorbidities?

Did you know? More than 25 percent of U.S. adults have two or more health conditions.

Man looking into medicine cabinet

“Comorbidities” isn’t the prettiest medical word, with “morbid” stuck there in the middle, but it comes up a lot in health care. Medically speaking, morbid just means related to a disease.

One study found “morbidity” was mentioned 25,000 times in a 10-year review of medical journal citations. That same article in the Annals of Family medicine noted that the term lacks a universally agreed upon definition and that doctors use other terms, such as “multimorbidity” and “patient complexity,” to mean roughly the same thing. A patient might hear that they have a comorbidity and wonder what it means.

Keeping it simple, comorbidity means that two or more diseases are present at once. So if someone who has diabetes also has high blood pressure, the high blood pressure would be considered a comorbidity. Especially in the elderly and people with complex medical problems, comorbidities are common. In the United States, more than 25 percent of adults have two or more of these 10 chronic conditions, according to the Centers for Disease Control and Prevention:

  • Arthritis
  • Cancer
  • Chronic obstructive pulmonary disease (COPD)
  • Coronary heart disease
  • Asthma
  • Diabetes
  • Hepatitis
  • Hypertension
  • Stroke
  • Weak or failing kidneys

Comorbidities came up a lot in coverage of the COVID-19 pandemic as researchers tried to figure out who would be especially at risk of getting seriously ill or dying. The findings were varied and not always in agreement, but COPD and chronic kidney disease are among conditions that received close scrutiny as risk factors. Another study, just released this summer, found the immunocompromised were more likely than others to be hospitalized with COVID-19. Some comorbidities can co-exist without much impact on your overall health. But others will interact and affect each other, which could be complicated further by medicines a patient might need to manage several conditions at once.

Certain prescription drugs might impact the effectiveness of other drugs, or the side effects of a drug might exacerbate another condition. It’s important for you and your doctor to be aware of comorbidities so that you can pursue effective treatments for your whole self, not just one condition at a time.

Some patients are surprised to learn that certain comorbidities make them ineligible for a clinical trial. It’s nothing personal. In a clinical trial, researchers are trying to control the variables so that they zero in on whether the potential treatment is making a real difference. Comorbidities can cloud the results when scientists are trying to establish cause and effect.

The most common comorbidities are also the most common diseases that affect people worldwide and in the U.S., like heart disease, obesity, diabetes and stroke. Comorbidities can be biologically linked, like when an underlying genetic risk relates to multiple conditions. For example, mental health conditions often co-occur, like ADHD, depression and anxiety. Likewise, people with one inflammatory disease will often have another, including Crohn’s disease, rheumatoid arthritis, asthma or psoriasis. These types of relationships between diseases can stem from shared genetic factors or similar disease pathways in the body.

Learn more about comorbidities for hemophilia, primary immune deficiencies, Alpha 1Antitrypsin Deficiency and hereditary angioedema.