Minoxidil

An antihypertensive agent indicated in severe arterial hypertension. Oral administration of 5 to 40mg daily in one or two doses, with the possibility of reaching 100mg daily. Low doses of oral Minoxidil, from 0.5 to 2.5 mg daily, and topiclal Minoxidil 2 - 5% are being used to treat alopecia in women. ^{(Sinclair 2018, Perera 2017)}

It is excreted in breastmilk in clinically insignificant amounts and no problems have been observed in an infant whose mother was taking it at an antihypertensive dose of 7.5 to 10 mg per day. ^{(Valdivieso 1985)}

The highest relative dose (RD) (5%) was obtained at the time of taking the medication, decreasing RD at three hours to 1.2%, at six hours to 0.3% and at nine hours to 0.1%. You can therefore minimize the risk by avoiding breastfeeding at the time of taking the medication, which is when the levels in milk are higher.

The low oral doses that are prescribed for the treatment of alopecia pose few problems for breastfeeding. 

Several medical societies, experts and expert consensus, consider the use of this medication to be safe or very probably safe during breastfeeding ^{(Malachias 2016)}. American Academy of Pediatrics: it is a medication which is usually compatible with breastfeeding. ^{(Malachias 2016, AAP 2001)}

Some authors do not consider it to be safe or only in case of breastfeeding older infants ^{(Anderson 2018)}. There are no published reports with antihypertensive doses greater than 10 mg per day, so in these cases, safer known alternatives may be preferable, especially in the neonatal period and in case of prematurity. ^{(Anderson 2018)}

TOPICAL USE:

The small dose and low plasma absorption of most topical dermatological preparations make transfer in significant amounts into breastmilk very unlikely. 
Only 1.4% (0.3-4.5%) of minoxidil reaches blood plasma when it is used topically on the skin. ^{(Butler 2014, Johnson 2014, Galderma 2013)}

A case of transient hypertrichosis on the forehead of a 2-month-old infant whose mother applied topical minoxidil 5% twice daily has been reported. The causality is not well clarified in the publication^{. (True 2022)}

It is normal to lose hair in the months following pregnancy and this has nothing to do with breastfeeding but with stopping the resting phase in hair loss that occurs during pregnancy. Within 12 months after delivery, the hair grows back without leaving alopecia.