Health Talk: Birth control changes release of hormones

Credit: Adelaide Cole/Art Editor Credit: Adelaide Cole/Art Editor

Both convenient and effective, birth control pills have become the most popular form of contraception used by women in the United States. According to the Centers for Disease Control, 17 percent of women aged 15 to 29 years currently use some form of birth control pill. states that certain birth control pills can be as much as 99 percent effective in preventing pregnancy. While most other forms of contraception try to prevent the sperm from reaching the egg, birth control pills work from within and create conditions within the body that make it unsuitable for pregnancy.

The female reproductive system is controlled by a set of tightly regulated hormones. Birth control pills essentially work by disrupting this intricate balance of hormones in the body. The two hormones found in birth control pills are estrogen and progestin. Estrogen is normally produced in females, as is progesterone, which is a less concentrated natural form of progestin. As explained on, estrogen normally helps in the release of eggs from the ovary in females. This allows the egg to travel further through the reproductive tract, where it may eventually intercept a sperm.

The body also has a system of keeping the estrogen secretion in check. Estrogen secretion is regulated by what is called a negative feedback loop. Large amounts of estrogen have a negative effect on its secretion and eventually cause the body to stop secreting estrogen. Progesterone is secreted later in the reproductive cycle and prepares the uterus for pregnancy. One of its major functions is to cause the thickening of the uterine lining, thus allowing the embryo to be implanted in the uterus wall for pregnancy. Like estrogen, progesterone is also regulated by a negative feedback loop and prevents its own secretion after a while.

Birth control pills make use of the fact that both estrogen and progesterone are regulated by negative feedback loops. By adding an excess amount of estrogen and progesterone in the body, birth control pills activate the negative-feedback loop and prevent the body from secreting estrogen and progesterone. Lack of estrogen production prevents the release of an egg from the ovary, and lack of progesterone causes the lining of the uterus to become thin and unsuitable for pregnancy.

As explained on, such pills generally fall into two categories: combination birth control pills and mini pills. Combination pills contain a mixture of estrogen and progestin, while mini pills contain only progestin. Since they contain both estrogen and progestin, combination pills prevent the release of eggs from the ovary and also make the uterus unsuitable for pregnancy. Hence, combination pills tend to be more effective and are a more popular option. However, excess estrogen can have a number of side effects on the body, which make combination pills unsuitable for some women. Most importantly, excess estrogen can cause blood clots to form. Hence, combination pills have the added risk of causing stroke and heart disease.

Mini pills are therefore recommended for those with pre-existing conditions like high blood pressure or those with a history of being susceptible to blood clots. However, since these pills contain only progestin, periodic release of eggs happens normally. Thus, when using mini pills there is a higher chance of unwanted pregnancies.

Both types of pills, however, carry the risks of causing headaches, cysts in the ovary, irregular menstrual patterns, and mood swings. The pills also do not protect against sexually transmitted diseases, and other forms of protection have to be used in order to prevent the spread of such diseases.

Until recently it was believed that contraceptive pills caused weight gain in women. However, according to a recent study published in the journal Human Reproduction, contraceptive pills do not cause women to gain weight.