Contraception
FAQ186, July 2014



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Progestin-Only Hormonal Birth Control: Pill and Injection

What is progestin?

Progestin is a form of progesterone, a hormone that plays a role in the menstrual cycle and pregnancy. Progestin is used in combination with another hormone called estrogen in combined hormonal birth control pills, the vaginal ring, and the skin patch. It also can be used by itself in progestin-only pills and the birth control injection. The birth control implant and the hormonal intrauterine device also are progestin-only forms of birth control and are discussed in FAQ184 Long-Acting Reversible Contraception (LARC): IUD and Implant. 

How effective are progestin-only pills and the birth control injection in preventing pregnancy?

Progestin-only pills and the injection have about the same effectiveness as combination estrogen and progestin pills, rings, and patches.

What are progestin-only pills?

Progestin-only pills contain progestin. They are available by prescription only.

How do progestin-only pills work?

Progestin-only birth control pills, sometimes called “mini-pills,” have several effects in the body that help prevent pregnancy:

  • The mucus in the cervix thickens, making it difficult for sperm to enter the uterus and fertilize an egg.
  • They stop ovulation, but they do not do so consistently. About 40% of women who use progestin-only pills will continue to ovulate.
  • They thin the lining of the uterus, making it less likely that a fertilized egg can attach to it.

What are the benefits of progestin-only pills?

  • They do not interfere with sex.
  • They may reduce menstrual bleeding or stop your period altogether.
  • They are not associated with an increased risk of high blood pressure or cardiovascular disease and can be taken even if you have certain health conditions that prevent you from taking combination pills, such as a history of  deep vein thrombosis or uncontrolled high blood pressure.
  • They can be used immediately after childbirth, even if you are breastfeeding.

What are possible risks of progestin-only pills?

Progestin-only pills may not be a good choice for women who have certain medical conditions, such as some forms of lupus. Women who have breast cancer or who have a history of breast cancer should not take progestin-only pills.

How do I take progestin-only pills?

The progestin-only pill comes in packs of 28 pills. All the pills in the pack contain progestin. Take one pill at the same time each day for 28 days. It is important to take the progestin-only pill at the exact same time each day for maximum effectiveness. Do not skip pills for any reason—even if you bleed between periods or feel sick.

What if I forget to take a pill?

If a pill is missed by more than 3 hours, you should take a pill as soon as possible and use a backup method of contraception (such as condoms) for the next 2 days. If vomiting or severe diarrhea occurs within 3 hours after taking a pill, the progestin may not be absorbed completely by your body. Keep taking your pills, but use a backup method until 2 days after your vomiting or diarrhea stops.

What are possible side effects of progestin-only pills?

Bleeding may be unpredictable. You may have short cycles of bleeding, spotting, or heavy bleeding or no bleeding at all. Other side effects include headaches, nausea, and breast tenderness.

What is the birth control injection?

The birth control injection is an injection of the hormone depot medroxyprogesterone acetate. It provides protection against pregnancy for 3 months.

How does the injection work?

The injection has several effects that work together to prevent pregnancy:

  • It stops ovulation.
  • It thickens and decreases the amount of cervical mucus. This makes it difficult for sperm to enter the uterus and fertilize an egg.
  • It thins the lining of the uterus, making it less likely that a fertilized egg can attach to it.

How is the injection given?

A health care provider must give the injection. The first shot can be given at any time during your menstrual cycle as long as you and your health care provider are reasonably sure you are not pregnant.

How often do I need injections?

You must return to your health care provider every 13 weeks for repeated injections. The repeat injection can be given up to 2 weeks late (15 weeks from the last injection). If it is given more than 2 weeks late, you will need to avoid sexual intercourse or use a backup method of birth control, such as condoms, for the next 7 days.

What are the benefits of the injection?

  • The injection does not need to be taken daily.
  • It does not interfere with sex or daily activities.
  • No one can tell you are using birth control.
  • It has several health benefits not related to birth control:

— Reduced risk of cancer of the uterus if used long term

— Possible protection against pelvic inflammatory disease

— Reduced pelvic pain caused by endometriosis

— Possible absence of periods

— Possible relief of certain symptoms of sickle cell disease and seizure disorders

— Possible decrease in bleeding associated with uterine fibroids

What are possible risks of the injection?

Bone loss may occur while using the birth control injection. When the injections are stopped, at least some and sometimes all of the bone that is lost is gained back. Women who have multiple risk factors for cardiovascular disease may be at increased risk of cardiovascular disease while using the injection. This increased risk may last for some time after the method is stopped. Women with a history of stroke, vascular disease, or poorly controlled high blood pressure also may be at increased risk of cardiovascular disease while using this method.

What are possible side effects of the injection?

The injection may cause irregular bleeding. Some women report weight gain while using progestin-only birth control methods. Among women who gained weight, the average amount of weight gained was less than 5 pounds. It takes an average of 10 months for pregnancy to occur after stopping the injection.

Glossary

Bone Loss: The gradual loss of calcium and protein from bone, making it brittle and more likely to fracture.

Cardiovascular Disease: Disease of the heart and blood vessels.

Cervix: The lower, narrow end of the uterus at the top of the vagina.

Deep Vein Thrombosis: A condition in which a blood clot forms in veins in the leg or other areas of the body.

Egg: The female reproductive cell produced in and released from the ovaries; also called the ovum.

Endometriosis: A condition in which tissue that lines the uterus is found outside of the uterus, usually on the ovaries, fallopian tubes, and other pelvic structures.

Estrogen: A female hormone produced in the ovaries.

Fibroids: Benign growths that form in the muscle of the uterus.

Hormone: A substance made in the body by cells or organs that controls the function of cells or organs. An example is estrogen, which controls the function of female reproductive organs.

Intrauterine Device: A small device that is inserted and left inside the uterus to prevent pregnancy.

Lupus: An autoimmune disorder that causes changes in the joints, skin, kidneys, lungs, heart, or brain.

Ovulation: The release of an egg from one of the ovaries.

Progesterone: A female hormone that is produced in the ovaries and that prepares the lining of the uterus for pregnancy.

Progestin: A synthetic form of progesterone that is similar to the hormone produced naturally by the body.

Sperm: A cell produced in the male testes that can fertilize a female egg.

Uterus: A muscular organ located in the female pelvis that contains and nourishes the developing fetus during pregnancy.

If you have further questions, contact your obstetrician–gynecologist.

FAQ186: Designed as an aid to patients, this document sets forth current information and opinions related to women’s health. The information does not dictate an exclusive course of treatment or procedure to be followed and should not be construed as excluding other acceptable methods of practice. Variations, taking into account the needs of the individual patient, resources, and limitations unique to the institution or type of practice, may be appropriate.

Copyright July 2014 by the American College of Obstetricians and Gynecologists