Oral Contraceptives / Birth Control Pills

Content written by Irwin Goldstein, MD

Oral contraceptives or birth control pills are hormonal medications that contain combinations of synthetic, non-biologically identical hormones, ethinyl estradiol and a progestin. This drug was developed to prevent pregnancy by modifying regulation and therefore the usual function of the woman’s ovary. Normally the ovary has two functions. One function is to develop a follicle and an egg and to release the egg during ovulation. The other ovarian function is to synthesize the biologically identical estradiol, 17-beta estradiol, which has actions all over the body on brain, muscle, bone, skin, hair, breast, external genitals, and uterus. Normally, two pituitary-based hormones, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) regulate the two functions of the ovary and their levels vary greatly throughout the menstrual cycle.

One mechanism whereby the synthetic hormones in the birth control pill achieve contraception is by pharmacologically suppressing or stopping the pituitary release of LH and FSH. Thus the birth control pill prevents both development of the follicle and ovulation, as well as the synthesis of the biologically identical 17-beta estradiol, that is normally synthesized by the woman’s ovary.

Suppression of the pituitary is achieved because the active synthetic estrogen in the birth control pill, ethinyl estradiol, binds with significantly higher affinity to the estradiol receptor compared to the normal, biologically identical 17-beta estradiol. It is estimated that ethinyl estradiol has 600 times more affinity to the estradiol receptor than 17-beta estradiol.

One significant consequence of the use of the synthetic, high affinity binding ethinyl estradiol is the dramatic rise in the liver synthesis of a very important protein call sex hormone binding globulin (SHBG). Women who use the oral contraceptive pill have on average a five to six fold increase in level of sex hormone binding globulin (SHBG), but this author has seen it as high as ten times that of women who have never used oral contraceptives.

The function of sex hormone binding globulin (SHBG) is to bind sex steroids such as testosterone in a storage form for future use, if needed. The problem arises that testosterone bound to SHBG is not biologically available to tissues. Women with SHBG levels five to six fold of normal SHBG have low levels of unbound or free testosterone. Thus the majority of women who use oral contraceptives also have low levels of free testosterone. This fact provides oral contraceptive users protection from acne, since acne is a free testosterone-mediated effect. But free testosterone has many other critical actions, especially on mood, energy, and sexual function. Some oral contraceptive users develop hormonally-mediated sexual dysfunction as a consequence of their using hormonally-mediated birth control.

Another consequence of the use of the synthetic, high affinity binding ethinyl estradiol is lowered levels of the normal estradiol, 17-beta estradiol. Some users of the oral contraceptive pill may develop atrophy of tissues, especially genital tissues that are hormonally responsive to 17-beta estradiol but may not be responsive in the same fashion to ethinyl estradiol.

It is important to consider both the positive and negative aspects of use of an oral or other hormonally-mediated birth control when making a decision about method of contraception. Alternatives to hormonally-mediated birth control include mechanical barriers such as condoms, diaphragms and intra-uterine devices. The decision should be made after being informed of all the aspects that both promote and contraindicate use of each method of contraception. There is no single contraception that is best for all people.

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