Physiologic Basis of the Different Types of Hormonal Birth Control

Hormonal contraception is a method of preventing pregnancy that acts on the endocrine system, which is essentially the body’s chemical messenger system. Administered via oral, patches, implants or depot injection method, hormonal birth control methods alter the level of estrogen and progestin analogs. The contraceptive effect is facilitated by negative feedback in the hypothalamus which leads to reduced secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH). This alteration obstructs the process of ovulation and ultimately prevents pregnancy. In other cases, progestin hormone thickens cervical mucus, decreases tubal motility, and inhibits endometrial proliferation, thus decreasing the chances of implantation. For each dosage, a woman may receive progesterone or a combination of estrogen and progesterone. A combination of the two hormones suppresses ovulation by inhibiting gonadotropin secretion.  Since hormonal contraceptives alter endometrial growth, they can theoretically block conception by impeding implantation.

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As discussed above, there are two types of contraceptives: Combination contraceptives and Progesterone-only contraceptives. The former contain progestin and estrogen. The role of progestin is to bind progesterone receptors. Combination contraceptives are the most widely used. Dosage is more often than not administered every day for three weeks after which placebo pills are administered in the remaining week of the month. It is common for users to experience withdrawal bleeds, which signifies that pregnancy has not occurred, in the week they are taking placebo pills. There are variants of combination pills that eliminate the use of placebo pills. Such pills are clinically suited for women who suffer from painful menstruation (dysmenorrhea) and excessive menstrual bleeding (menorrhagia). It is important to note that steroid hormones are nonpolar. Thus, they may be delivered topically (applying them to body surfaces like the skin or mucous membranes). Combination contraceptives that are administered via this method comprise a patch that is replaced on a weekly basis and a vaginal ring that is worn for three weeks for replacement.

Progesterone-only contraceptives exist in two variants: low-dose pills and long-acting methods. Low-dose pill methods may be effective for women who want to avoid pregnancy in short time spans while long-acting methods are suited for those who cannot or do not want to remember to take a regular dose. Low-dose pills are less effective than combination contraceptives and are primarily aimed at preventing ovulation. Their effectiveness is subject to the ability of progesterone to alter cervical mucus. As a result, it is necessary for the user to take these contraceptives regularly, preferably at the same time every day. This ensures that the plasma level of progestin is enough for altering cervical mucus. The low-dose pill method is recommended for women who want to avoid estrogen or those who are lactating and don’t want to become pregnant since high progesterone and estrogen levels can inhibit milk synthesis. The long-acting variant of progesterone-only contraceptive is the most effective type of hormonal contraception. These methods comprise an injection that is given once every 3 months, intrauterine device that releases a progestin, and an implantable rod that secretes progestin. The implantable rod and intrauterine device are more effective as they work for years once they are inserted. The method works by releasing a steady dose of progestin which prevents ovulation via negative feedback inhibition.

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