Although the word progesterone refers to a substance that maintains pregnancy, progesterone is secreted as part of the normal menstrual cycle.

The corpus luteum of the ovary secretes large amounts of progesterone after ovulation, and the adrenal cortex secretes small amounts.

The hormone circulates in the blood attached to a specific plasma protein. It is metabolized in the liver and conjugated for excretion in the bile.

The local effects of progesterone on reproductive organs include the glandular development of the lobular and alveolar tissue of the breasts and the cyclic glandular development of the endometrium.

Progesterone also can compete with aldosterone at the level of the renal tubule, causing a decrease in sodium reabsorption, with a resultant increase in secretion of aldosterone by the adrenal cortex, as occurs in pregnancy.

Although the mechanism is uncertain, progesterone increases basal body temperature and is responsible for the increase in body temperature that occurs with ovulation.

Smooth muscle relaxation under the influence of progesterone plays an important role in maintaining pregnancy by decreasing uterine contractions and is responsible for many of the common discomforts of pregnancy, such as edema, nausea, constipation, flatulence, and headaches.

The increased progesterone present during pregnancy and the luteal phase of the menstrual cycle enhances the ventilatory response to carbon dioxide, leading to a measurable change in arterial and alveolar carbon dioxide (PCO2) levels.

Referrence:Female Internal Genitalia||Progesterone(Chinese Version)

What does it do? Progesterone is a hormone from a corpus luteum, formed by the cyclical rupture of an ovarian follicle. Progesterone is necessary for proper uterine and breast development and function.

Natural progesterone and synthetic progestins are structurally different and have differing effects in the body. Progestins are recommended by doctors if estrogen is prescribed during or after menopause, because prolonged estrogen replacement therapy without the addition of progestins (or large amounts of natural progesterone), increases the risk of uterine cancer.1 However, women who have had a hysterectomy¡ªand therefore no longer have a uterus¡ªare typically prescribed estrogens without progestins. Although natural progesterone is considered by some doctors to be safer and more effective for a variety of health problems, researchers have studied the effects of supplemental natural progesterone much less than the effects of synthetic progestins.

Preliminary evidence suggests that progesterone plays a role in bone metabolism and could help reduce the risk of osteoporosis.2 An uncontrolled study, using topically applied natural progesterone cream in combination with diet, exercise, and vitamin and calcium supplementation, reported consistent gains in bone density over a three-year period in postmenopausal women. However, no comparison was made to a similar program without progesterone.3

One trial found that adding natural progesterone to estrogen therapy had no better effect on bone mass than estrogen therapy alone4 and another trial reported that progesterone applied topically over a one-year period had no effect on bone loss.5 Thus no consistent support for the use of topical progesterone in the treatment or prevention of osteoporosis has appeared in published research.

Some doctors have observed that progesterone administered vaginally, rectally, or topically (to the skin) can relieve the symptoms of premenstrual syndrome (PMS).6 However, most well-controlled studies have not found natural progesterone to be effective against PMS.7

One double-blind study found that topical administration of natural progesterone led to a reduction in hot flashes in 83% of women, compared with improvement in only 19% of those given a placebo.8 Synthetic progestins have also been reported to reduce symptoms of menopause.9

Some studies have linked synthetic progestins to increased risk of breast cancer.10 In contrast, topical progesterone has produced changes in breast tissue that may have a cancer prevention effect.11 12 Other researchers, however, have reported essentially opposite effects, suggesting that natural progesterone may increase proliferation of breast cells.13

Looked at as a whole, the research remains incomplete and inconsistent. In one trial, (natural) progesterone deficiency was linked with an increased risk, but only when the breast cancer was diagnosed before menopause.14 Such a finding fits with the idea that natural progesterone might be protective. This position is further strengthened by a preliminary trial showing that a raised level of progesterone in the blood at the time of breast cancer surgery is associated with an improved prognosis for premenopausal women with operable breast cancer.15 However, most breast cancer begins postmenopausally, and one trial found that progesterone deficiency was associated with a large (though statistically nonsignificant) decreased risk of postmenopausal breast cancer.16 If duplicated by future research, this finding would not suggest protection, nor even necessarily safety.

A recent report found that long-term topical use of natural progesterone on the breast neither increased nor decreased the risk of women eventually being diagnosed with breast cancer.17 In this trial, some women were also taking oral synthetic progesterone-like drugs. Remarkably, women using this combination experienced a 50% decreased risk of eventually being diagnosed with breast cancer. More research is needed to understand the effects of both synthetic and natural progesterone in both pre- and postmenopausal women.

Synthetic progestins have been linked to effects that might increase the risk of heart disease.18 However, vaginally applied natural progesterone has been reported to significantly enhance the benefits of estrogen replacement therapy on heart function in women with coronary artery disease.19 More research is needed to evaluate the effects of natural progesterone on heart disease.

Although the differences in the chemical structure of natural progesterone and synthetic progestins are slight, their effects in the body differ considerably and the two forms should not be considered interchangeable. Synthetic progestins may be useful for endometriosis and menorrhagia (prolonged or profuse menstrual flow) because of their specific effects on progesterone receptors in the brain and on the glandular response of the uterine lining. However, these same effects may be detrimental for women with PMS, and may be associated with increased symptoms, such as depression, headaches, and water retention. Thus, natural progesterone may be preferable to synthetic progestins for PMS.20

Where is it found? Progesterone is produced in the female body in the ovaries. Progesterone production is high during the luteal phase (second portion) of the menstrual cycle and low during the follicular phase (first portion), as well as being low before puberty and after menopause.

Supplemental sources of progesterone are available in oral and cream forms, as well as lozenges, suppositories, and injectable forms. ¡°Natural¡± progesterone refers to the molecule that is identical in chemical structure to the progesterone produced in the body, even if the molecule is synthesized in a laboratory.

Progestins are found in oral contraceptive pills and are used in conventional hormone replacement therapy.

Wild yam contains precursors to progesterone (such as diosgenin) that can be converted through a chemical process in the laboratory into progesterone¡ªthe exact same molecule made in the human body. However, contrary to popular claims, the diosgenin in wild yams cannot be converted into progesterone in the body.21 22 Women who require progesterone should consult their physician and not rely on wild yam or other herbs.

Pregnenolone, another hormone produced by the body, is converted by the body into progesterone. However, it is not clear what effect supplementing with pregnenolone will have on progesterone production in the body.

Who is likely to be deficient? Postmenopausal women have reduced production of progesterone. While this ¡°deficiency¡± is normal, progesterone, including the natural forms of progesterone, has been found to relieve menopausal symptoms when used in combination with estrogen replacement therapy.23

How much is usually taken? The proper amount of progesterone for a woman should be determined in consultation with a doctor. Some research with the natural, oral form of progesterone has used 200 mg per day.24 Progesterone is used in much lower amounts¡ªsuch as 20¨C70 mg per day¡ªby most doctors who prescribe topical natural progesterone. However, the ability of skin-applied progesterone to achieve effective levels in the body is the source of considerable debate.25 Although progesterone is a natural substance, oral progesterone supplements are available by prescription only. High-dose topical progesterone cream is also treated like a drug and requires a prescription. A few creams containing lower amounts of progesterone are sold without prescription.

Are there any side effects or interactions? Progesterone is a hormone and, as such, concerns about its inappropriate use have been raised. A physician should be consulted before using this hormone as a supplement. Few side effects have been associated with topical progesterone creams but can include skin reactions. Effects of natural progesterone on breast cancer risk remain unclear. Research has suggested both increased and reduced risk.

Synthetic progestins have many well-known side effects, including the increase of LDL (¡°bad¡±) cholesterol and the decrease of HDL (¡°good¡±) cholesterol. Other side effects reported with synthetic progestins include bloating, breast soreness, depression, and mood swings. Natural progesterone has been shown to have no adverse effect on HDL cholesterol levels.26 Overall, natural progesterone is considerably safer than progestins and is therefore preferred by many doctors in situations where either would be effective.27

At the time of writing, there were no well-known drug interactions with progesterone.