Medzhitov was born in Tashkent, Uzbekistan, and earned a B.S. at Tashkent State University before going on to pursue a Ph.D. in biochemistry at Moscow University in 1990. At that time the Soviet Union was disintegrating and funding for science was drying up. Because laboratories were short of supplies, Medzhitov spent much of his time in the library, reading about modern biomedical science.
There, he came upon a paper by Yale immunobiologist Charles Janeway (now deceased), who was studying how the innate immune system, an evolutionarily ancient system found in all multicellular animals, interacts with the adaptive immune system, found only in vertebrates. Medzhitov wrote to Janeway and was accepted for postdoctoral study at Yale, arriving in 1994. The two researchers made the groundbreaking discovery that Toll-like receptors, a component of the innate system, provide the adaptive system with the necessary information to create custom-made B and T cells that target specific bacterial or viral invaders.