Inhibin A is a dimer of alpha and beta A subunits, inhibin B is a dimer of alpha and beta B subunits. Inhibin belongs to the transforming growth factor-β superfamily.In women, FSH stimulates the secretion of inhibin from the granulosa cells of the ovarian follicles in ovary. In turn, inhibin suppresses FSH.Inhibin secretion is diminished by GnRH, and enhanced by insulin-like growth factor-1.Inhibin A reaches its peak in the mid-luteal phase.

Inhibin-A is elevated in the blood serum of women carrying fetuses with Down syndrome.Inhibin is produced in the gonads, ituitary gland, placenta and other organs.In men, it is a hormone that inhibits FSH production.The inhibin alpha subunit joins either the beta A or beta B subunit to form a pituitary FSH secretion inhibitor.