One of Chang's notable achievements was his research and testing of the effectiveness of certain orally administered steroids in the control of mammalian fertility. Thism lead to his co-invention of the first birth control pill with Gregory Pincus. Chang is arguably most remembered for this endeavor as the birth control pill came to have a tremendous influence on human society and the sexual revolution. However, controlling fertility was not the primary concentration of his work. Chang's interest lay in sperm, eggs, and the fertilisation process itself. The ability to control the fertility of eggs was a necessity to his work. He initiated the study of orally administered contraceptives for mammals to enable him to better conduct his research in fertilisation. Indeed, throughout the span of his 45-year career, only five years, 1951 to 1956, were spent researching and testing the effectiveness of orally administered contraceptives, and this work was mainly on the oral mode of the administration of the contraceptive steroids, rather than on the effectiveness of the steroids themselves, which had already been previously proven.