Oxytocin

Oxytocin is an endogenous hormone with a cyclic nonapeptide structure. It is secreted by the hypothalamus and stored in the posterior lobe of the pituitary gland.
It is an essential hormone during childbirth and lactation and it is released during breastfeeding producing a calming and anxiolytic effect on the mother (Niwayama 2017).
It is present in men and women even during the neonatal period and its natural form has been found in breast milk (Lawrence 2016 p77).
Causes uterine contractions and has a mild antidiuretic effect.

The bioavailable synthetic form is used to induce labor, support delivery of the placenta and control postpartum bleeding (Uptodate 2018).
Oxytocin is administered intravenously and intranasally through various dosing protocols (ACOG 2009, Leduc 2013, Wei 2010, Uptodate 2018).

At the date of the last update, we did not find published data on its excretion in breast milk.

Pharmacokinetic data (moderately high molecular weight and acidic pKa) make it unlikely for oxytocin to pass into breast milk in significant quantities (Hale 2017 p741).
Due to its proteinaceous nature it is inactivated in the gastrointestinal tract without being absorbed (oral bioavailability practically nil: De Groot 1995) and this hinders or prevents passage to neonatal and infant plasma from ingested breast milk (Apotex 2018, Alfasigma2018, Hale 2017 p741). Circulating oxytocin in neonatal / infant plasma is endogenously produced (Lawrence 2016 p77).

USE OF OXYTOCIN DURING DELIVERY
The induction of labor with oxytocin is widespread and has known risks (Guerra 2009).
There is controversy about how exogenous oxytocin during labor can affect endogenous secretion and lactation. Even though there is little research with limited methodologies and of very heterogeneous consistencies (Erickson 2017, Buckley 2015), several studies suggest that intravenous oxytocin administered during childbirth can affect breastfeeding altering primitive reflexes and reducing neonatal breastfeeding behaviour responses, delaying or hindering the start or duration of lactation (Marin 2015, Brimdyr 2015, Bell 2013, Abdoulahi 2017, Gomes 2018, García 2014, BBrown 2014, Bell 2013, Olza 2012, Wiklund 2009).
Other research has not found this association (Takahashi 2021, Fernández 2019 and 2017), especially if the administration of oxytocin is not accompanied by epidural analgesia (Takahashi 2021) or when long-term results are measured. The possible adverse effects of synthetic intrapartum oxytocin do not persist beyond the first few days: the administration of intrapartum oxytocin decreases the probability of exclusive breastfeeding on discharge from the maternity, but does not affect the duration or type of breastfeeding at 6 weeks or 9 months postpartum (Takács 2021).

USE OF OXYTOCIN AS GALACTOGOGUE
Oxytocin has been used as a galactogogue (Winterfeld 2012) with very different results. One trial with significant methodological flaws found an important increase in production (Ruis 1981) and in another trial there was no difference in milk production between the two evaluated groups (Fewtrel 2006).
A series of 3 cases of tetraplegic mothers with loss of neuronal connection between breast and hypothalamus reported a favorable effect on milk letdown with the use inhaled oxytocin (Cowley2005).

The chronic use of intranasal oxytocin can lead to dependence, so its use should be limited to the first week postpartum (Hale 2017 p741).

The best galactogogue is a frequent on-demand lactation with correct technique and a mother that retains her self-confidence (Mannion 2012, Forinash 2012, ABM 2011). Do not use as a galactogogue without sanitary control.

Oxytocin does not improve the symptoms of breast engorgement in the immediate puerperium (Mangesi 2016, Ingelman-Sundberg1953).