Eating disorders are often chronic and relapsing disorders, and AN has the highest death rate of any psychiatric disorder. Research demonstrates that 55–97% of people diagnosed with an eating disorder also receive a diagnosis for at least one more psychiatric disorder such as: depression, anxiety disorder, schizophrenia, systemic developmental disorders. The lack of understanding of the pathogenesis of eating disorders has hindered the development of effective interventions. The present study, after a introduction on the physiology of the oxytocin system, we summarize current evidence on oxytocin's role in the regulation of food intake and in pathophysiology and treatment of eating disorders and other psychiatric conditions.

Oxytocin (OXT) is a peptide neurohormone composed of nine amino acids, with a molecular weight of 1007, synthesized by the supraoptic nucleus (SON) and paraventricular nucleus (PVN). Released from the PVN, OXT participates in its communication with other structures of the central nervous system (CNS), e.g. the spinal cord, while released from the dendrites of neurosecretory cells, it affects structures located in the vicinity of the hypothalamus, e.g. the limbic system (Veening and Olivier, 2013). Another route of OXT communication is through the long axons of the neurosecretory nuclei reaching the neural part of the pituitary gland from where it is secreted into the circulatory system (Chruścicka et al., 2021; Liu et al., 2022).

Secretion of OXT occurs by reflex, as a result of stimulation of the nipples, uterine receptors, and also hormonal, stimulated by estrogen. It is a hormone that performs numerous regulatory functions in the body. The most well-known effect is its participation in uterine contraction during labor, in the transport of sperm toward the fallopian tubes, and in the ejection of milk during lactation (Bakos et al., 2018; Wójciak et al., 2012). Nevertheless, research shows that it also acts at the CNS level, regulating emotional and cognitive processes, maternal instincts and sexual behavior (Dumais and Veenema, 2016). In addition, it is one of the primary biological determinants of social behavior related to the formation of attachment, such as between mother and child, and during pairing (Liu et al., 2022; Dumais and Veenema, 2016). OXT has been shown to reduce cortisol release and anxiety levels in response to social stress in individuals who have never been diagnosed with a mental disorder (Heinrichs et al., 2003). In addition, it reduces the activity of the amygdala in stress-related reactions and also increases confidence in giving money (Domes et al., 2007). Responses to acute stressors include the release of OXT presumably in anticipation of more chronic situations that may occur, facilitating passive forms of coping and protecting against shutdown or “fear immobilization” (Engert et al., 2016). In addition, positive effects on empathy levels and improvements in the ability to interpret mental states have been described, as well as prolonged eye gazing while looking at faces (Domes et al., 2007; Guastella et al., 2008). Patients with mental disorders – including eating disorders often show impairments of psychological and psychological functions related with OXT secretion. Against this backdrop, it may be hypothesized that oxytocin plays a role in the connection between psychosocial functions and ingestive behavior.

OXT is also implicated in the control of control of energy balance. It has turned out to be a downstream mediator of the effects of leptin, an anorexigenic product of white fat cells that signals to the brain how much energy is stored as body fat (Altirriba et al., 2015) Moreover leptin has been shown to target a specific subpopulation of OXT neurons in paraventricular nucleus (PVN), and its effects are important for leptin's ability to reduce body weight in both control and obese rats (Perello and Raingo, 2013). Secretion of OXT from a descending PVN to nucleus of the solitary tract pathway contributes to leptin's attenuation of food intake by a mechanism that involves the activation of paraventricular nucleus oxytocin neurons by leptin, resulting in increased sensitivity of nucleus of the solitary tract neurons to satiety signals (Blevins et al., 2004). What is more mRNA levels of oxytocin, vasopressin, and somatostatin were reduced by fasting and restored by leptin in PVN (Tung et al., 2008).

OXT has been used for many years primarily in gynecology, to initiate or enhance uterine contractions during labor or to accelerate uterine contractions and reduce bleeding after delivery. During labor, OXT is administered by intravenous route (Bomba-Opoń et al., 2017). Intranasal spray application is not suitable for induction, it is only applicable postpartum, to stimulate lactation. The biological half-life in plasma is 1–6 min and is prolonged at the end of pregnancy and during lactation. The onset of action of OXT occurs immediately after intravenous administration and decreases within 1 h, 3–5 min after intramuscular administration and persists for 2–3 h. Excretion occurs via the kidneys and liver, with only a small portion of the hormone being excreted unchanged in the urine.

In recent years, scientific work on the effects of OXT on neural tissue has suggested that its role extends far beyond birth and lactation by playing an important role in psychiatric disorders. Both human and animal studies have consistently shown that intranasal administration of OXT affects the processing of emotional stimuli and exerts anti-anxiety effects, most likely by modulating amygdala activity. In the vast majority of studies, 24 international units (IU) of OXT were administered intranasally and measured approximately 45 min later. Enteral and parenteral administration are not adequate because the oral route involves inactivation of the hormone in the gastrointestinal tract and first-pass metabolism in the liver, whereas parenteral injections are unlikely to cross the blood-brain barrier and are associated with severe cardiovascular side effects at high doses.

Studies show the involvement of OXT in the etiology of psychiatric disorders such as eating disorders, major depression (MD), postpartum depression (PPD), schizophrenia, autistic spectrum disorders (ASD), and addiction, and on its potential use in the diagnosis of these diseases and treatment (Dumais and Veenema, 2016). However, the exact role of OXT in psychiatric disorders requires further research. The purpose of the following publication is to review the results regarding the use of OXT in the treatment of selected psychiatric disorders with particular emphasis on eating disorders and to determine the practical relevance of OXT in clinical practice.