While studies have demonstrated conflicting results about the effects of COCPs on lactation duration and milk volume, there exist concerns about the transient risk of COCPs on breast milk production when breastfeeding is being established early postpartum. Due to the stated risks and additional concerns on lactation, women who are breastfeeding are not advised to start COCPs until at least six weeks postpartum, while women who are not breastfeeding and have no other risks factors for blood clots may start COCPs after 21 days postpartum. Breast cancer
The WHO currently does not recommend the use of COCPs in women with breast cancer. Since COCPs contain both estrogen and progestin, they are not recommended to be used in those with hormonally-sensitive cancers, including some types of breast cancer. Non-hormonal contraceptive methods, such as the Copper IUD or condoms, should be the first-line contraceptive choice for these patients instead of COCPs. Other
Women with known or suspected endometrial cancer or unexplained uterine bleeding should also not take COCPs to avoid health risks. COCPs are also contraindicated for people with advanced diabetes, liver tumors, hepatic adenoma or severe cirrhosis of the liver. COCPs are metabolized in the liver and thus liver disease can lead to reduced elimination of the medication. Additionally, severe hypercholesterolemia and hypertriglyceridemia are also currently contraindications, but the evidence showing that COCPs lead to worse outcomes in this population is weak. Obesity is not considered to be a contraindication to taking COCPs.
Combined hormonal contraceptives, including COCPs, inhibit follicular development and prevent ovulation as a primary mechanism of action.Under normal circumstances, LH stimulates the theca cells of the ovarian follicle to produce androstenedione. The granulosa cells of the ovarian follicle then convert this androstenedione to estradiol. This conversion process is catalyzed by aromatase, an enzyme produced as a result of FSH stimulation. In individuals using oral contraceptives, progestogen negative feedback decreases the pulse frequency of gonadotropin-releasing hormone (GnRH) release by the hypothalamus, which decreases the secretion of follicle-stimulating hormone (FSH) and greatly decreases the secretion of luteinizing hormone (LH) by the anterior pituitary. Decreased levels of FSH inhibit follicular development, preventing an increase in estradiol levels. Progestogen negative feedback and the lack of estrogen positive feedback on LH secretion prevent a mid-cycle LH surge. Inhibition of follicular development and the absence of an LH surge prevent ovulation.Estrogen was originally included in oral contraceptives for better cycle control (to stabilize the endometrium and thereby reduce the incidence of breakthrough bleeding), but was also found to inhibit follicular development and help prevent ovulation.