What Is It?
Progesterone is a hormone that stimulates and regulates important functions, playing a role in maintaining pregnancy, preparing the body for conception and regulating the monthly menstrual cycle.
Progesterone is one of the hormones in our bodies that stimulates and regulates various functions. Progesterone plays a role in maintaining pregnancy. The hormone is produced in the ovaries, the placenta (when a woman gets pregnant) and the adrenal glands. It helps prepare your body for conception and pregnancy and regulates the monthly menstrual cycle. It also plays a role in sexual desire.
During the reproductive years, the pituitary gland in the brain generates hormones (follicle-stimulating hormone [FSH] and luteinizing hormone [LH]) that cause a new egg to mature and be released from its ovarian follicle each month. As the follicle develops, it produces the sex hormones estrogen and progesterone, which thicken the lining of the uterus. Progesterone levels rise in the second half of the menstrual cycle, and following the release of the egg (ovulation), the ovarian tissue that replaces the follicle (the corpus luteum) continues to produce estrogen and progesterone.
Estrogen is the hormone that stimulates growth of the uterine lining (endometrium), causing it to thicken during the pre-ovulatory phase of the cycle.
The Role of Progesterone in Women
One of progesterone's most important functions is to cause the endometrium to secrete special proteins during the second half of the menstrual cycle, preparing it to receive and nourish an implanted fertilized egg. If implantation does not occur, estrogen and progesterone levels drop, the endometrium breaks down and menstruation occurs.
If a pregnancy occurs, progesterone is produced in the placenta, and levels remain elevated throughout the pregnancy. The combination of high estrogen and progesterone levels suppress further ovulation during pregnancy. Progesterone also encourages the growth of milk-producing glands in the breast during pregnancy.
High progesterone levels are believed to be partly responsible for symptoms of premenstrual syndrome (PMS), such as breast tenderness, feeling bloated and mood swings. When you skip a period, it could be because of failure to ovulate and subsequent low progesterone levels.
The word "progestogen" refers to any hormone product that affects the uterus in much the same way as our natural progesterone. Effective synthetic versions of progesterone, called progestins, have been around since the 1950s. A micronized capsule version of natural progesterone (derived from wild yams) was developed more recently.
Progestogens are included along with estrogen in combination oral contraceptives and in menopausal hormone therapy. Progestins are also used alone for birth control and for treatment of a variety of other conditions, including abnormal uterine bleeding and amenorrhea (absence of periods); endometriosis; breast, kidney or uterine cancer; and loss of appetite and weight related to AIDS and cancer. Progestins may also be used as a diagnostic aid to check the effects of estrogen.
Birth Control Pills
Combination birth control pills (pills that contain both estrogen and progestin) block ovulation and make the body less receptive to a fertilized egg during ovulation. The pills typically have to be taken in a specified order. When the hormones are stopped during the placebo or "dummy" pills, a withdrawal bleed occurs.
Some birth control pills, called mini-pills, contain only progestin. These pills do not always suppress ovulation, but make the cervical mucus thick and unwelcoming to sperm, preventing entry to the uterus. They also thin the endometrial lining, making it less receptive to a fertilized egg. Mini-pills are slightly less effective than combination pills but are still a very effective form of contraception when used properly.
Progestin is also the active ingredient in the long-acting injected contraceptive Depo Provera (medroxyprogesterone) and the intrauterine device (IUD) Mirena.
Maintaining menstrual cycles, a function of progestins, is important during childbearing years because unopposed estrogen without progesterone increases the risk of endometrial cancer. If you frequently skip periods due to polycystic ovary syndrome (PCOS), being overweight or underweight, or another disorder, your health care professional may recommend birth control pills to regulate your cycle.
If you miss periods and can't take either combination or progestin-only birth control pills, or would simply prefer not to take them, you may need an occasional progestin prescription to balance the unopposed estrogen. This will also result in the shedding of the uterine lining at least four times a year.
As you grow older and enter perimenopause (the menopause transition phase, which can last six years or more and ends one year after your final menstrual period), your hormone levels fluctuate and decrease, causing irregular ovulation and menstruation, as well as bothersome symptoms like hot flashes. Some women find that low-dose birth control pills can help control perimenopausal symptoms and keep periods regular.
After menopause (which occurs at an average age of 51), you will probably produce only a fraction of the amount of estrogen as you did before menopause.
Latest News on Hormone Therapy and Estrogen Therapy
Supplemental menopausal hormone therapy (either estrogen therapy [ET] alone or a combination of estrogen-progestin therapy, known as hormone therapy [HT] or menopausal hormone therapy [MHT]) has long been recommended as one option for women to consider for relief of menopausal symptoms and to prevent bone loss. The progestin in HT is included primarily to protect the uterine lining. Estrogen stimulates growth of the endometrium (the uterine lining), creating a risk for uterine precancers and cancer, and should be taken alone, or "unopposed," only if you have had a hysterectomy.
The U.S. Food and Drug Administration (FDA) now advises health care professionals to prescribe menopausal hormone therapies at the lowest possible dose and for the shortest possible length of time to achieve treatment goals. If you are taking hormones, you should re-evaluate your treatment with your health care professional every six months.
Ask your health care professional for more information about the latest research on ET and HT, and how the risks and benefits of using these therapies apply to your personal health needs.
There now are lower-dose hormone therapies available. These include Prempro 0.3/1.5 and Prempro 0.45/1.5 with lower doses of estrogen and progestin, as well as Climara PRO, femhrt, Activella and Angeliq. These medications are lower-dose products than the Prempro product used in the Women's Health Initiative, which suggested increased risks of some health conditions like breast cancer and heart disease for certain women taking one particular type of hormone therapy.