Disease is an impairment of the normal state or one of its parts that interrupts or modifies the performance of the vital functions. Disease is a disturbance of homeostasis or steady state within an organism. The disease spectrum is the range of the disease states represented by the diseased individuals (acute vs. chronic or convalescent cases, mild vs. severe cases, clinical vs. subclinical). According to one popular medical dictionary, “disease” means “any deviation from or interruption of the normal structure or function of any part, organ, or system (or combination thereof) of the body that is manifested by a characteristic set of symptoms and signs and whose etiology, pathology, and prognosis may be known or unknown.” An asymptomatic condition does not exclude disease since the presence of signs (laboratory, radiological, etc.) will connote disease. These include diseases such as hypertension, hypercholesterolemia, hypogonadism, and infertility.

Every disease has a range of manifestations and a natural history that varies from individual to individual. Pathophysiology is a term that refers to the disorder or breakdown of the human body’s function. Three aspects of a disease process form a framework for understanding pathophysiology. They are (1) the cause or etiology of the disease, (2) pathogenesis of the mechanism of its development, and (3) clinical manifestations representing the structural and biochemical alterations in the body and the functional consequences of these changes.

It is inarguable that in medicine, an adverse effect is a harmful and undesired effect resulting from a medication or other intervention. An adverse effect or side effect (when judged secondary to a main or therapeutic effect) may result from an unsuitable or incorrect dosage or procedure (which could be due to medical error). Adverse effects are sometimes “iatrogenic” because they are physician/treatment generated. Some adverse effects only occur only when starting, increasing, or discontinuing a treatment. Adverse effects may cause medical complications of a disease or procedure and negatively affect its prognosis. They may also lead to non-compliance with a treatment regimen.

Indications of a harmful outcome is usually by some result such as morbidity, mortality, body weight alteration, enzyme levels, loss of function, or a pathological change detected at the microscopic, macroscopic, or physiological level. Other indications include symptoms reported by a patient. Adverse effects may cause a reversible or irreversible change, including an increase or decrease in the susceptibility of the individual to other disease.