How the Birth Control Pill Works

Types of Birth Control Pills

There are three different types of oral contraceptive pills: combination, progestin-only or extended-release.

The combination pill is the one most commonly used, but the progestin-only pill, also known as the "minipill," is a better choice for some women -- women who are breastfeeding, for example, can't take a pill with estrogen because it affects their milk supply. Some examples of minipill brands include Micronor, Femulen and Microval.

The minipill prevents pregnancy in two ways: It makes the endometrium too thin to accept a fertilized egg and makes the vaginal mucus too thick to allow sperm to reach the egg. It's slightly less effective than the combination pill, and women taking it are more likely to experience spotting. Taking the minipill means taking 28 active pills every month, and it's even more important to take it on time to avoid the risk of pregnancy.

As far as the combination pill goes, there are three main subtypes:

  • Monophasic pills have the same amount of hormones in all 21 pills. They're the most commonly prescribed combination pill because they're very simple to take -- they're all the same color, and if a woman misses one, she can easily double up the next day. Some brand names include OrthoCyclen, Alesse and Loestrin.
  • Biphasic pills alternate between two different levels of hormones and are lower in hormones overall. Examples include Mircette and Ortho Novum 10/11.
  • Triphasic pills alternate between three different hormone levels. Tri-Levelen, Ortho TriCyclen and Triphasal are some examples.

All types contain 21 active pills. (Some brands also include seven days of inert pills to be taken during the week of menstruation.) They all contain the same type of synthetic estrogen, called ethinyl estradiol, but vary in the type of progestin they use. The main difference is that some women who experience unpleasant side effects on monophasic pills might do better on biphasic or triphasic pills.

Rather than wait seven days between active pills, some women simply start over with the 21 day pill cycle when on a monophasic pill to avoid having a period.

Next we'll look at the newest type of the pill.