Oxytocin

Oxytocin is a natural hormone made in the brain (the hypothalamus) and released from the pituitary. It's familiar as the 'bonding hormone,' but its actions are concrete and well-defined.

It works through the oxytocin receptor on smooth muscle and in the brain. In the body it makes the uterus contract during labor and triggers milk let-down during breastfeeding — the basis for its approved obstetric uses. In the brain it acts on circuits in the amygdala and reward system involved in trust, bonding, and social behavior, the focus of much current research.

Its obstetric dosing is well established by labeling, but the behavioral and social uses — often studied with a nasal spray — remain investigational and far less settled than the headlines suggest.