Ask Doctor K: Hormones are responsible for bith control side effects

DEAR DOCTOR K: I started taking combined birth control pills a few months ago. Ever since then, I sometimes feel nauseous and get severe headaches. Should I switch to a different pill?

DEAR READER: Nausea and headaches are common side effects of birth control pills, but they usually can be eliminated by adjusting the pills.

Combined birth control pills contain the hormones estrogen and progestogen. When taken correctly, they are 98 percent to 99 percent effective in preventing pregnancy. But these hormones can cause side effects.

Birth control pills work in different ways. The estrogen in birth control pills prevents ovulation: the release of a mature egg from a woman’s ovary. Without the release of the egg, pregnancy can’t happen. Progestogen has other effects to prevent pregnancy that we will explore below.

The normal menstrual cycle is 28 days, and ovulation occurs at about day 14. Oral contraceptives packages usually contain 21 active tablets and seven inactive pills. This maintains a 28-day cycle.

Here’s how the estrogen works to block ovulation: Normally, the body’s natural estrogen levels rise from day one through about day 12, and then start falling. The falling estrogen signals the brain to produce luteinizing hormone. This hormone travels in the blood from the brain to the ovaries, and encourages the ovaries to release an egg.

Birth control pills contain estrogen through about day 21. Thus, estrogen levels don’t fall around day 12, the brain does not produce LH, and an egg is not released.

The progestogen in birth control works to prevent pregnancy in several ways. It thickens cervical secretions, making it difficult for sperm to get into the uterus. It causes changes in the fallopian tubes. And it makes it hard for a fertilized egg to implant in the uterus.

The amount of estrogen and progestogen in your birth control pills affects the likelihood of side effects. The secret is to get the right balance – just enough to prevent pregnancy, but not enough to cause side effects.