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Progestin-only Contraceptives

The progestin only birth control pill is also known as the mini pill and can be used by women who experience unacceptable side effects from the use of estrogen-containing oral contraceptives. It may also be used by women who have medical conditions which prevent the use of estrogen-containing contraceptives. This includes women who are breastfeeding or who have migraine headaches.

How does the mini pill work?

The mini pill contains about one-half the progesterone found in most combined oral contraceptive pills. There is no estrogen in these pills. Approximately 50% of the women who take the mini pill continue to ovulate. The effectiveness of the mini pill depends primarily on the changes in the cervical mucus. The mucus becomes thicker, preventing the sperm from penetrating through the cervix to fertilize the egg.

The lower dose of the mini pill means that it is important that the pill be taken daily and at the same time every day. Some clinics recommend that a back-up method be used for the woman's first three cycles while using the mini pill.

What are the advantages of the mini pill?

• The mini pill is approximately 97% effective at protecting against unwanted pregnancy and is fully reversible.
• As with the combined birth control pills, women who take the mini pill have less premenstrual discomfort.
• It has also been shown that using the mini pill may be protective against pelvic inflammatory disease and endometrial and ovarian cancer.
• Because the mini pill contains no estrogen, a woman theoretically has a lower risk of blood clot formation and heart attacks compared to a woman taking the combined oral contraceptive pill. There are no studies, however, to document this.

What are the disadvantages/ side effects of the mini pill?

Overall, the mini pill is less effective than the combined oral contraceptives in protecting against pregnancy. The combined birth control pill is approximately 99% effective, while the mini pill is approximately 97% effective when used perfectly. In the first year of use, however, the possibility of pregnancy is 5%.

Many women experience some change in their bleeding pattern when taking the mini pill. Spotting can occur in up to 25% of women, or women may stop having periods. This is most common when a woman has been on the mini pill for longer than six months. The absence of a period is not harmful; nonetheless, the first time a woman misses a period, it is important for her to come in for evaluation to make sure she is not pregnant.

• Some women experience minor headaches, nausea, weight gain, depression, and cramping.
• Some studies have demonstrated that taking progesterone alone may cause an increase in cholesterol.
• If you do become pregnant while taking the mini pill, you have a slightly higher chance that the pregnancy will be ectopic (outside of the womb).
• Ovarian cysts are more common among mini pill users. The cysts usually disappear without treatment and rarely cause problems.

Important instructions for mini pill users:

Have a back-up birth control method such as condoms with spermicide or a diaphragm available. You will need to use your back-up method for the first month.

• Take one pill each day until you finish your pill pack. Then start your new pack the next day. Never miss a day. Find a regular time each day you will remember to take the pill.
• If you are late or miss taking your pills, take the missed pill as soon as you remember that you missed it. Take your scheduled pill at the regular time even if that means taking two pills in one day. If you are more than three hours late taking the mini pill, there is a good chance you could become pregnant. Use your back-up birth control method for the next 48 hours. You may want to call the consulting nurse to discuss emergency contraception.
• If your menstrual period does not begin within 4-6 weeks, see your clinician for a pregnancy test.
• Keep track of your periods while you take mini pills. If you go more than 45 days without a period, see your clinician for an exam and pregnancy test.
• If you have spotting or bleeding between periods, keep taking your mini pills on schedule. If your bleeding is heavy or associated with cramps or fever, please see your clinician.
• If you become ill with vomiting, severe diarrhea, or both, use your back-up method of birth control along with your mini pills until 48 hours after your illness is over.
  If you decide you want to become pregnant, plan to stop using mini pills and change to another method of birth control for 2-3 months to identify how frequently your menstrual period comes.
• See your clinician regularly for routine check-ups. Be sure to have an annual Pap smear, breast exam, pelvic exam, and blood pressure check.

Certain drugs taken at the same time as birth control pills can make them less effective. Such drugs also may cause an increase in breakthrough bleeding. This more commonly occurs with medications for epilepsy and the anti-tuberculosis drug, rifampin. If another medication is prescribed while you are taking the pill, talk with your health care provider and your pharmacist about possible problems from taking these medications together.

Danger signs to watch out for when using birth control pills:

Call the clinic immediately or consult your private doctor or local emergency room if you experience:

• Severe headaches
• Visual changes (flashing lights in the eyes, blurriness, partial loss of vision, other unusual visual changes)
• Numbness or tingling in the face, arm, leg, hand, or foot
• Sharp pain in the chest, shortness of breath, or coughing up blood (these symptoms may indicate possible clots in the lung)
• Severe leg pain (possible clot in the leg)
• Crushing chest pain or heaviness (possible heart attack)
• Severe abdominal pain.

These symptoms may a warning sign of a blood clot, heart attack or stroke. 

Problems and Questions

If you have any questions, you may call a consulting nurse for further information:

Primary Care Unit: (206) 221-2517
Women's Clinic: (206) 685-1031
After Hours Consulting Nurse (206) 744-2500

Last updated: 02/11/07
Last reviewed: 08/09