Radiopharmaceuticals, or medicinal radiocompounds, are a group of pharmaceutical drugs containing radioactive isotopes. Radiopharmaceuticals can be used as diagnostic and therapeutic agents. Radiopharmaceuticals emit radiation themselves, which is different from contrast media which absorb or alter external electromagnetism or ultrasound. Radiopharmacology is the branch of pharmacology that specializes in these agents.

Nuclear medicine is the study and utilization of radioactive compounds in medicine to image and treat human disease. It relies on the ‘tracer principle’ first espoused by Georg Karl von Hevesy in the early 1920s. The tracer principle is the study of the fate of compounds in vivo using minute amounts of radioactive tracers which do not elicit any pharmacological response by the body to the tracer. 

A radioactive tracer, radiotracer, or radioactive label is a chemical compound in which one or more atoms have been replaced by a radionuclide so by virtue of its radioactive decay it can be used to explore the mechanism of chemical reactions by tracing the path that the radioisotope follows from reactants to products. Radiolabeling or radiotracing is thus the radioactive form of isotopic labeling. In biological contexts, use of radioisotope tracers are sometimes called radioisotope feeding experiments.

NUCLEAR MEDICINE IMAGING procedures look at the bodily functions to help make the diagnosis.

NUCLEAR MEDICINE THERAPY can actually be used to treat the body. If patients are undergoing a therapy process, then larger amounts of radiation will be used to treat different types of malignant diseases or thyroid disease. . 

Nuclear medicine is a medical specialty that uses radioactive tracers (radiopharmaceuticals) to assess bodily functions and to diagnose and treat disease. Specially designed cameras allow doctors to track the path of these radioactive tracers.