Contraceptive pills are commonly used by women for birth control due easiness of administration, their effectiveness among others. A single pill may contain either oestrogen, progesterone or both hormones (combined oral contraceptive) which are also found in the body. They inhibit ovulation and create an environment not suitable for implantation of the fertilized egg in the uterus (uterus). For one to increase chances of getting pregnant, she must have unprotected sexual intercourse at least 3 times per week. Effectiveness of these oral pills depend on the user

As commonly used, about 8 pregnancies occur per 100 women using pills over the first year. This means that 92 of every 100 women using pills will not become pregnant. When no pill-taking mistakes are made, less than 1 pregnancy per 100 women using pills will occur over the first year that is 3 per 1,000 women

Here are some of the causes of contraceptive failure which is manifested as occurrence of pregnancy despite actively using the pills

  1. Risk of pregnancy is greatest when a woman starts a new pill pack 3 or more days late, or misses 3 or more pills near the beginning or end of a pill pack. A full pack contains 21 hormone containing pills and 7 non hormone pills containing iron
  2. Not using another back up birth control method (like condoms or diaphragm) in addition to using pills in the first 7 days when the woman has just started the pill method. Backup should be done for at least 7 days whilst taking the pills. However, if started in within 5 days after onset of menstrual periods, or immediately after an abortion, or switching from hormonal implants, there’s no need for a backup method.
  3. Concurrent medical conditions affecting the alimentary canal causing persistent vomiting, diarrhea or inadequate absorption function of the intestines. Since these pills are taken orally, they pass through the stomach, to the intestines to be absorbed into the blood stream and finally to target organs for action. These conditions reduce chances of absorption hence causing lower drug blood levels
  4. Concurrent taking of certain medications with pills. Examples include some drugs used of treating tuberculosis, epilepsy, depression and HIV. These drugs increase breakdown of the contraceptive pills hence reducing blood concentrations by inducing certain liver enzymes. Reporting to the health care providers about use of these drugs can help in dosage adjustments or other alternatives
  5. Swallowing pills which are expired or poorly stored under unfavourable conditions. Since these pills are “chemicals”, their chemical properties are affected by the environment and this may render them pharmacologically ineffective