Ethinyl Estradiol and Breastfeeding

Summary of use during lactation

This record contains information specific to ethinyl estradiol used alone. Users with an interest in an oral contraceptive should consult the record entitled, record entitled, Contraceptives, Oral, Combined. There is little information available on the use of ethinyl estradiol alone during breastfeeding. The concentration in milk is negligible with dosses of 35 mcg or less daily. Based on studies on oral contraceptives that contain ethinyl estradiol, immediate side effects such as breast enlargement appear to occur rarely. It seems likely that doses of 30 mcg daily or greater can suppress lactation. The magnitude of the effect on lactation likely depends on the dose and the time of introduction postpartum. It is most likely to occur if the estrogen is started before the milk supply is well established at about 6 weeks postpartum. The decrease can happen over the first few days of estrogen exposure.[1]

Drug levels in milk and infant serum

Maternal Levels. Four women who were fully nursing their infants were given a contraceptive containing ethinyl estradiol 50 mcg and megestrol acetate 4 mg beginning at 2 months postpartum. Another 4 women who were 6 to 18 months postpartum were given a single dose of 500 mcg of ethinyl estradiol. After 10 days of therapy, ethinyl estradiol was undetectable (<50 ng/L) in the milk of women who received the 50 mcg dose at several times after the dose. In those who receive 500 mcg, peak milk levels usually were found in the 3-hour sample although the peak was found in the 7-hour sample in one. Peak milk levels ranged from about 170 to 300 ng/L; levels dropped rapidly and were usually undetectable by 23 hours after the dose. Based on the higher dose, the authors estimated that a fully breastfed infant whose mother was taking 50 mcg of ethinyl estradiol daily would receive a dose of about 10 ng daily.[1] Milk was collected and pooled from 2 groups of women who were taking ethinyl estradiol 100 mcg 3 times daily either immediately postpartum or after 1 to 6 months postpartum. Milk samples were collected 2 hours after the dose. Pooled milk was bioassayed for estrogenic activity and compared with the milk from lactating mothers taking no exogenous estrogens whose milk was collected at various times postpartum. No estrogenic activity was detected (<10 ng/80 mL of pooled milk [<0.125 mcg/L]) from women taking ethinyl estradiol above background estrogenic activity found in control colostrum.[2] A study measured ethinyl estradiol in the milk of 14 breastfeeding women: 6 using combined oral contraceptives (15, 20, or 30 mcg daily of ethinyl estradiol), 7 using a vaginal ring (15 mcg daily of ethinyl estradiol), and 1 using a transdermal patch (35 mcg daily of ethinyl estradiol). A control group of 8 breastfeeding women not using hormonal contraceptives was also included. Ethinyl estradiol was undetectable (<3.5 mcg/L) in all of the women.[3] Infant Levels. Relevant published information was not found as of the revision date.

Effects in breastfed infants

Published information was not found as of the revision date on the effects of ethinyl estradiol alone on breastfed infants. However, case reports exist of breast enlargement in the infants of mothers taking combination oral contraceptives that contained ethinyl estradiol or its prodrug, mestranol.[1,4,5]

Effects on lactation and breastmilk

Published information was not found as of the revision date on the effects of ethinyl estradiol on milk production. However, numerous studies on combination contraceptives containing ethinyl estradiol or its prodrug mestranol indicate that doses of 30 mcg daily or greater might interfere with lactation.[6-11] One study that used a contraceptive containing 10 mcg of ethinyl estradiol found no effect on lactation.[12] A retrospective cohort study compared 371 women who received high-dose estrogen (either 3 mg of diethylstilbestrol or 150 mcg of ethinyl estradiol daily)during adolescence for adult height reduction to 409 women who did not receive estrogen. No difference in breastfeeding duration was found between the two groups, indicating that high-dose estrogen during adolescence has no effect on later breastfeeding.[13]

Alternative drugs to consider

Estradiol

References

1. Nilsson S, Nygren KG, Johansson ED. Ethinyl estradiol in human milk and plasma after oral administration. Contraception 1978;17:131-9630883 PubMed
2. Betrabet SS, Shikary ZK, Toddywalla VS, et al. ICMR Task Force Study on hormonal contraception. Biological activity of ethinyl estradiol present in the breast milk. Contraception 1986;34:169-753780231 PubMed
3. Segev L, Ben Zimra A, Weitzman GA, et al. Ethinylestradiol transfer into breast milk of women using low-dose combined hormonal contraception is negligible. Open Access J Contracept 2025;16:189-9741399541 PubMed
4. Madhavapeddi R, Ramachandran P. Side effects of oral contraceptive use in lactating women - enlargement of breast in a breast-fed child. Contraception 1985;32:437-434085247 PubMed
5. Marriq P, Oddo G. Gynecomastia in the newborn induced by maternal milk? An unusual complication of oral contraceptives. Nouv Presse Med 1974;3:2579
6. Kaern T. Effect of an oral contraceptive immediately post partum on initiation of lactation. Br Med J 1967;3:644-56038336 PubMed
7. Guiloff E, Ibarra-Polo A, Zanartu J, et al. Effect of contraception on lactation. Am J Obstet Gynecol 1974;118:42-54128673 PubMed
8. Peralta O, Díaz S, Juez G, et al. Fertility regulation in nursing women: V. Long-term influence of a low-dose combined oral contraceptive initiated at day 90 postpartum on lactation and infant growth. Contraception 1983;27:27-386404597 PubMed
9. Croxatto HB, Díaz S, Peralta O, et al. Fertility regulation in nursing women: IV. Long-term influence of a low-dose combined oral contraceptive initiated at day 30 postpartum upon lactation and infant growth. Contraception 1983;27:13-256404596 PubMed
10. Díaz S, Peralta O, Juez G, et al. Fertility regulation in nursing women: III. Short-term influence of a low-dose combined oral contraceptive upon lactation and infant growth. Contraception 1983;27:1-116404595 PubMed
11. Nilsson S, Mellbin T, Hofvander Y, et al. Long-term follow-up of children breast-fed by mothers using oral contraceptives. Contraception 1986;34:443-573816229 PubMed
12. Toddywalla VS, Joshi L, Virkar K. Effect of contraceptive steroids on human lactation. Am J Obstet Gynecol 1977;127:245-9835620 PubMed
13. Jordan HL, Bruinsma FJ, Thomson RJ, et al. Adolescent exposure to high-dose estrogen and subsequent effects on lactation. Reprod Toxicol 2007;24:397-40217531440 PubMed