Inhibin is an endocrine hormone produced in the ovaries, the testes and the placenta. This hormone has several functions in the body, with inhibin levels in women being linked to the menstrual cycle and playing a role in fetal development. Another hormone, activin, has an action in the body opposite to that of inhibin. Levels of these two hormones tend to fluctuate in both men and women in response to a number of cues which can include changes in hormone levels triggered by natural biological processes, environmental pressure, and other factors.