The combined oral contraceptive pill (COCP), often referred to as the birth control pill or colloquially as "the pill", is a type of birth control that is designed to be taken orally by women. It is the oral form of combined hormonal contraception. The pill contains two important hormones: a progestin (a synthetic form of the hormone progestogen/progesterone) and estrogen (usually ethinylestradiol or 17β estradiol). When taken correctly, it alters the menstrual cycle to eliminate ovulation and prevent pregnancy. Combined oral contraceptive pills were first approved for contraceptive use in the United States in 1960, and remain a very popular form of birth control. They are used by more than 100 million women worldwide including about 9 million women in the United States. From 2015 to 2017, 12.6% of women aged 15–49 in the US reported using combined oral contraceptive pills, making it the second most common method of contraception in this age range (female sterilization is the most common method). Use of combined oral contraceptive pills, however, varies widely by country, age, education, and marital status. For example, one third of women aged 16–49 in the United Kingdom use either the combined pill or progestogen-only pill (POP), compared with less than 3% of women in Japan (as of 1950–2014). Combined oral contraceptives are on the World Health Organization's List of Essential Medicines. The pill was a catalyst for the sexual revolution.
Background
Oral contraceptives
Hormonal oral contraceptives are preventive medications taken orally by females to avoid pregnancy by manipulating their sex hormones. The first oral contraceptive was approved by the US Food and Drug Administration (FDA) and sold to the market in 1960. There are two types of hormonal oral contraceptives, namely combined oral contraceptives and progesterone-only pills. Oral contraceptives, whether combined or progesterone-only, can effectively prevent pregnancy by regulating hormonal changes in the menstrual cycle, inhibiting ovulation, and altering cervical mucus to impede sperm mobility; combined pills have extra effects in menstrual cycle regulation and menstrual pain relief. Common off-label uses include menstrual suppression and acne relief, with combined oral contraceptives having additional benefits in relieving menstrual migraines.
Variants Progesterone-only pills (POPs) utilise progestin, the synthetic form of progesterone, as the only active pharmaceutical ingredient in the formulation. In the US, drospirenone and norethindrone are the most commonly used compounds in formulations. Combined oral contraceptives (COCs) are commonly classified into generations, referring to their order of development in history. This discussion may also help identify some key features in a variety of products. According to the European Medicines Agency, the first generation of combined oral contraceptives, which made use of a high concentration of estrogen only, were those invented in the 1960s. In the second generation of products, progestogens were introduced into the formulation while the concentration of estrogen was reduced. Starting from the 1990s, the progression in the development of combined oral contraceptives has been directed towards varying the type of progestogen incorporated. These products are referred as the third and fourth generation. Estrogen ingredients: estradiol, ethinylestradiol, estetrol. 1st generation progestin: norethindrone acetate, ethynodiol diacetate, lynestrenol, norethynodrel. 2nd generation progestin: levonorgestrel, dl-norgestrel. 3rd generation progestin: norgestimate, gestodene, desogestrel.
The menstrual cycle
Hormonal oral contraceptives (HOCs) interact with hormonal changes in the menstrual cycle in females to prevent ovulation, and hence achieve contraception. In a 28-day menstrual cycle, there are the proliferative phase, ovulation, and then the secretory phase. Menstruation marks the beginning of proliferative phase in day 1-14. In this period, the pituitary gland located near the brain secretes follicle-stimulating hormone (FSH) into the bloodstream to signal the development of follicle in ovary in the female reproductive system. While follicle serves as the chamber of ovum development, it secretes estrogen, a hormone that not only triggers the thickening of uterine lining in preparation for implantation, but also inhibits the secretion of FSH in pituitary via a negative feedback mechanism. Specifically in ovulation, transient positive feedback by estrogen on FSH and luteinizing hormone (LH) secretion from pituitary is permitted so that the release of mature ovum from follicle is triggered. In secretory phase on day 14-28, this follicle then transforms into corpus luteum and continues releasing estrogen with progesterone into bloodstream. While estrogen and progesterone primarily aid the maintenance of thickness in uterine lining, the negative feedback in pituitary allows them to inhibit FSH and LH secretion. In the absence of LH, corpus luteum degenerates and ultimately causes blood estrogen and progesterone levels to decline. Without these thickness maintaining agents, uterine lining breaks down and hence the presentation of menstruation.
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