Author: Simone Maimon
Editors: Sophia Chen, Junyu Zheng
Artist: Emily Hu
Whether you’re looking to recover from a sickness, grow a few inches taller, or prevent a pregnancy, drugs are one of the most convenient ways to control how your body works. We can mass produce drugs that contain hormones—chemical signals that signal to specific cells; in most cases, doctors can prescribe medication to resolve the issues that arise in the human body. And just like a prescription drug, birth control uses hormonal methods that are convenient, effective, and reversible. On average, birth control has an efficacy rate of about 91% (this accounts for those who misuse it), whereas condoms have an efficacy rate of 85%. But how do birth control hormones affect one’s body? What hormones are manipulated to control the reproductive system?
In hormonal birth control, the most common type includes a mix of estrogen and progesterone, two important hormones that work together to maintain the reproductive system. There are three types of estrogen that are produced mainly by the ovaries and adrenal glands. Estrone is the estrogen that starts being produced after menopause and can transform into any of the other two types of estrogen, mainly because of the low levels of estrogen many post-menopausal women have The second type, estradiol, is primarily in the body during and after puberty because it increases transcription, or protein production, in certain reproductive cells responsible for promoting the growth of the vaginal and fallopian tube lining alongside the cervical glands. Additionally, it regulates uterine development, such as the buildup of the endometrium and the myometrium (uterine smooth muscle), and facilitates the growth of eggs in the ovary. Besides the gonadal effects of estradiol, it also plays major roles across the entire body by managing breast development, fat deposition, and bone density. The last type of estrogen is estriol, produced during pregnancy, which is important for uterine growth and prepares the body for breastfeeding.
Besides estrogen, the primary hormone in most birth controls is progesterone (or progestin), which also handles thyroid function and mood regulation. The ovary produces progesterone after ovulation to induce uterine changes to prepare for a pregnancy. It mainly thickens the uterine lining in preparation for egg fertilization, and if the ovulated egg doesn't get fertilized, the body stops producing progesterone, where the lining sheds during menstruation (A.K.A. a period). Birth control changes progesterone levels mainly because it inhibits the secretion of two other hormones: follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Normally, a spike in FSH causes a spike in LH, which ultimately signals the ovaries to release an egg. However, high progesterone after ovulation signals the hypothalamus—the part of the brain that regulates some hormone levels—to decrease FSH levels to prevent further ovulation. Ultimately, the progesterone in birth control tricks the body into not ovulating at all, meaning no egg can be fertilized and cause a pregnancy.
Because estrogen and progesterone are integral to our reproductive system’s health, birth control comes with its side effects. Birth control can cause spotting, breast swelling, nausea, changes in appetite, and other unexpected effects. Some types of birth control only affect progesterone levels, which may help avoid unwanted side effects caused by changes in estrogen. At the same time, the hormones altered by birth control can also lighten periods, prevent anemia, treat PCOS and endometriosis, reduce cramps, and lower the risk for certain types of cancer. Therefore, even those not looking to avoid pregnancy often get prescribed a “birth-control” type of pill. Hormones are extremely useful to control what happens within our body, but sometimes, these universal chemical messengers can drastically alter other parts; even now, scientists are still studying the extent to which birth control affects the human body.
Citations:
Cooper, Danielle B. “Oral Contraceptive Pills.” StatPearls [Internet]., U.S. National Library
of Medicine, 29 Feb. 2024,
www.ncbi.nlm.nih.gov/books/NBK430882/#:~:text=The%20progestogen-
“Birth Control Pill: Types, Side Effects & Effectiveness.” Cleveland Clinic, 1 May 2024,
“Estrogen: Hormone, Function, Levels & Imbalances.” Cleveland Clinic, 17 Sept. 2024,
“Contraception: Hormonal Contraceptives.” InformedHealth.Org [Internet]., U.S. National
Library of Medicine, 29 June 2017, www.ncbi.nlm.nih.gov/books/NBK441576/.
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