Oxytocin

Oxytocin is a 9-amino-acid hormone made in the hypothalamus, famous as the chemistry behind labor contractions, breastfeeding, and social bonding. As an injectable drug it is FDA-approved to induce labor and control postpartum bleeding, but the intranasal 'love hormone' versions sold for trust, anxiety, and autism are experimental and the human results are genuinely mixed. Oxytocin acts on a single G-protein-coupled oxytocin receptor found in the uterus, breast tissue, and many brain regions including the amygdala. In the periphery the receptor triggers calcium release that contracts uterine smooth muscle and the milk-ejection reflex. In the brain, oxytocin signaling modulates circuits involved in fear, social attention, and reward.