A complication in medicine, or medical complication, is an unfavorable result of a disease, health condition, or treatment. Complications may adversely affect the prognosis, or outcome, of a disease. Complications generally involve a worsening in the severity of the disease or the development of new signs, symptoms, or pathological changes that may become widespread throughout the body and affect other organ systems. Thus, complications may lead to the development of new diseases resulting from previously existing diseases. Complications may also arise as a result of various treatments.

The development of complications depends on a number of factors, including the degree of vulnerability, susceptibility, age, health status, and immune system condition. Knowledge of the most common and severe complications of a disease, procedure, or treatment allows for prevention and preparation for treatment if they should occur.

Complications are not to be confused with sequelae, which are residual effects that occur after the acute (initial, most severe)[1] phase of an illness or injury. Sequelae can appear early in the development of disease or weeks to months later and are a result of the initial injury or illness. For example, a scar resulting from a burn or dysphagia resulting from a stroke would be considered sequelae.[2] In addition, complications should not be confused with comorbidities, which are diseases that occur concurrently but have no causative association. Complications are similar to adverse effects, but the latter term is typically used in pharmacological contexts or when the negative consequence is expected or common.

Common illnesses and complications

Iatrogenic complications

Medical errors can fall into various categories listed below:[3]

Cardiovascular complications

Atrial fibrillation

Atrial fibrillation is a type of arrhythmia characterized by rapid and irregular heart rhythms due to irregular atrial activation by the atrioventricular (AV) node.[7] In the pathogenesis of atrial fibrillation, there is no effective pumping of blood into either the pulmonary or systemic circulation from the left ventricle of the heart. The left and right ventricles (lower chambers of the heart) do not fill properly due to the irregular contraction of the left and right atria (upper chambers of the heart).[7]

A patient with atrial fibrillation may experience symptoms of fatigue, dizziness or lightheadedness, heart palpitations, chest pain, and shortness of breath.[7][8] The heart does not effectively pump blood into the pulmonary or systemic vasculature, and causes the blood to remain within the chambers of the heart.[8][9] The collection of blood within the heart due to atrial fibrillation can cause and increase the risk of development of a thrombus (blood clot).[9] The thrombus can also develop into an embolus (mobile blood clot) and travel into the systemic circulation.[9] Atrial fibrillation is associated with an increase in risk of having a stroke especially if the embolus travels to the brain.[9]

Other examples

Metabolic complications

Diabetes mellitus

Diabetes mellitus, also known simply as diabetes, is a disorder of the regulation of blood glucose (a common type of sugar) levels. There are two types of chronic diabetes mellitus: type I and type II. Both lead to abnormally high levels of blood glucose as the body is not able to properly absorb the sugar into tissues. Diabetes requires a life-long consistent monitoring of food intake, blood sugar levels, and physical activity. Diabetes mellitus may present a series of complications in an advanced or more severe stage, such as:

Neurologic / psychiatric complications

Reproductive complications


Pregnancy is the development of an embryo or fetus inside the womb of a female for the rough duration of 9 months or 40 weeks from the last menstrual period until birth.[31] It is divided into three trimesters, each lasting for about 3 months. The first trimester is when the developing embryo becomes a fetus, organs start to develop, limbs grow, and facial features appear.[32] The 2nd and 3rd trimesters are marked by a significant amount of growth and functional development of the body.[31] During this time, the woman's body undergoes a series of changes and many complications may arise involving either the fetus, the mother, or both.[33]

Ectopic pregnancies can lead to various complications during pregnancy including miscarriage and stillbirth.

Respiratory complications

Streptococcal pharyngitis

White exudates at the back of the mouth, a manifestation of strep throat.

Streptococcal pharyngitis, also known as strep throat, is an infection of the respiratory tract caused by group A Strep, Streptococcus pyogenes, a gram-positive, cocci, beta-hemolytic (lyses blood cells) bacteria.[42] It is primarily spread by direct contact and the transfer of fluids via oral or other secretions and manifests largely in children.[42] Common symptoms associated with streptococcal pharyngitis include sore throat, fever, white excretions at the back of the mouth, and cervical adenopathy (swollen lymph nodes underneath the chin and around the neck area).[43] Streptococcal pharyngitis can lead to various complications[44] and recurrent infection can increase the likelihood. In many of these, lack of treatment[45] and the body's immune response is responsible for the additional adverse reactions.[46] These include:[44]

Image of a surgical site infection caused by stitching

Surgical / procedural complications

Other examples of complications

See also


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Further reading

  • Coventry BJ (2014). Surgery: Complications, Risks and Consequences. Book series, seven volumes. Springer.
  • Mulholland MW, Doherty GM (2006). Complications in Surgery. Lippincott Williams and Wilkins. ISBN 978-0-7817-5316-6.
  • Gawande A (2002). Complications: A Surgeon's Notes on an Imperfect Science. Macmillan.