An estimated 8 out of 100 women taking combination birth control pills will get pregnant in the first year of use. Although taking combination birth control pills during early pregnancy doesn't increase the risk of birth defects, it's best to stop taking birth control pills as soon as you suspect you're pregnant.

Combination birth control pills won't protect you from sexually transmitted infections.

Combination birth control pills can cause side effects such as:

  • Breakthrough bleeding or spotting (more common with continuous or extended-cycle pills)
  • Breast tenderness
  • Decreased libido
  • Elevated blood pressure
  • Headaches
  • Mood changes
  • Nausea

Some side effects — including nausea, headaches, breast tenderness and breakthrough bleeding — may last only a few months or be less noticeable if you take the pill at the same time every day.

Combination birth control pills increase the risk of certain conditions. Some of these complications can be serious. They include the following:

  • Blood clots in the legs (recent studies suggest that the type of progestin used in the pill may affect the risk of blood clots, with pills containing drosperinone showing a higher risk)
  • Gallbladder disease
  • Heart attacks and stroke (smoking greatly increases the risk of these complications)
  • Liver tumors

Consult your health care provider as soon as possible if you're taking combination birth control pills and have:

  • Abdominal pain
  • Breast lump
  • Chest pain
  • Depression
  • Difficulty speaking
  • Eye problems, such as blurred or double vision or loss of vision
  • Fainting
  • Jaundice (yellowish discoloration of the skin)
  • New or worsening headaches
  • Seizure
  • Severe allergic skin rash
  • Severe leg pain or swelling
  • Severe mood swings
  • Two missed periods or signs of pregnancy
Nov. 18, 2011