Oxytocin. Polarised light micrograph of crystals of the female hormone oxytocin. In women this hormone is secreted naturally by the pituitary gland. It is also manufactured synthetically in the laboratory for use as a drug. Oxytocin causes contractions of the uterus during labour, and it also stimulates the flow of milk in women who are breast-feeding. As a drug it may be used to induce childbirth, or to help to expel the placenta. Oxytocin may be given in the form of a nasal spray to help increase milk flow while breast-feeding. Object-size: 6.0 mm.