Oxytocin

Oxytocin is a nine-amino-acid peptide with a disulfide ring, made in the hypothalamus and released from the posterior pituitary into the blood and within the brain. Its classical jobs are milk let-down and uterine contraction in labour; in animals and people it has also been linked to sexual and maternal behaviour, pair bonding, anxiety, trust, sociability and food intake, all through one receptor [1].

Childbirth. Intravenous or intramuscular oxytocin 10 IU is the World Health Organization's recommended drug for preventing postpartum haemorrhage, the leading cause of maternal death worldwide. In a 2025 Cochrane network meta-analysis, adding ergometrine or misoprostol to oxytocin reduced bleeding of 500 mL or more further than oxytocin alone [2]. Its short half-life on continuous infusion makes it easy to control when inducing labour [8].

Trust and social cognition. A 2005 study reported that intranasal oxytocin made people more willing to trust strangers with money [9]. A registered replication with more than 95% power, run by some of the same authors, found no effect [6]. A statistical analysis of the field concluded that intranasal oxytocin studies are generally underpowered and that most published findings are probably false positives [10]. A meta-analysis of 33 studies found one dose improved recognition of basic emotions, particularly fear, in healthy people, but had no effect on emotion processing in clinical groups [11].

Autism. In the largest trial, 290 children and adolescents took nasal oxytocin (target 48 IU a day) or placebo for 24 weeks; social withdrawal, other social measures and IQ did not differ [4]. In 106 Japanese adults, 6 weeks at 48 IU a day did not improve the primary social measure more than placebo, though repetitive behaviour and eye gaze to faces improved [12]. A higher-bioavailability spray showed an inverted-U dose response with a possible benefit at 6 units a day [13]. A 2026 meta-analysis of 42 trials across mental disorders found no significant overall effect, with a small signal in schizophrenia [14].

Sexual function. In 30 women with sexual dysfunction, oxytocin sprayed before sex for 8 weeks improved sexual function scores, but no more than placebo, which improved them just as much [7]. In 29 healthy couples, a single 24 IU dose did not change sexual drive, arousal, erection or lubrication, but increased orgasm intensity and contentment afterwards, particularly in men; the effects were small to moderate [15].

Weight. In 61 adults with obesity, 24 IU four times a day for 8 weeks did not change weight, body fat, visceral fat or liver fat, although people ate less at a test meal [5]. A pilot crossover trial in 13 young people with hypothalamic obesity also found no significant weight change [16]. A pilot in 21 older adults with sarcopenic obesity reported 2.25 kg more lean mass and lower LDL cholesterol than placebo [17].

The oxytocin receptor is a G protein-coupled receptor that can signal through Gq or Gi, activating pathways including MAPK, PKC, PLC and CaMK. In the brain, oxytocin neurons project to anxiety- and stress-regulating circuits such as the amygdala, the bed nucleus of the stria terminalis and the prefrontal cortex [1]. In the uterus the same receptor drives contraction [2].

How much of a nasal dose reaches the brain has been a central question. In people given 24 IU intranasally, oxytocin rose in the cerebrospinal fluid by 75 minutes, but plasma and CSF levels did not track each other [3]. Oxytocin also has an antidiuretic effect, so intravenous doses can cause water retention [18].

Intranasal oxytocin has been well tolerated in trials. In the 24-week paediatric autism trial the incidence and severity of adverse events were similar to placebo [4]. A meta-analysis of long-term use in autism found nasal discomfort, tiredness, irritability, diarrhoea and skin irritation, none more common than on placebo [20]. In adults with obesity taking it four times a day for 8 weeks, there were no serious adverse events and no difference from placebo [5]. One adult in an autism trial developed temporary breast enlargement [12]. In young people with hypothalamic obesity, nosebleeds, nasal irritation, headache, nausea and changes in heart rate, blood pressure and QTc interval were similar on oxytocin and placebo [16].

In obstetrics, where doses are larger and given intravenously, oxytocin can overstimulate the uterus and cause cardiovascular events [8]. Its antidiuretic effect can cause water intoxication with severe low sodium, even on low-dose labour regimens [18].