Prolactin is secreted by the pituitary gland. There are only two major functions of prolactin: to induce milk production and to develop nerve cells. Higher levels of prolactin have been associated with tumors involving the lungs, the pituitary gland, and the kidneys. Prolactin is sometimes used by doctors to evaluate sexual dysfunction of unknown cause in both men and women. It seems higher levels of prolactin may disrupt normal orgasm. Drugs, supplements and certain diseases may disrupt normal prolactin blood levels. These include hypothyroidism, antidepressants, estrogen, opioid pain killers, diuretics, and L-arginine.