Progesterone

Progesterone is one of the two primary female hormones. As the name implies, progesterone prepares (pro) the womb for pregnancy (gestation). Progesterone works in tandem with estrogen; indeed, if estrogen is taken as a medication without being balanced by progesterone (so called unopposed estrogen), there is an increased risk of uterine cancer. However, progesterone is not well absorbed orally. For this reason, pharmaceutical manufacturers developed progestins, substances similar to progesterone which are more easily absorbed. Most of the time, a woman prescribed progesterone is really being given a progestin. Two of the most commonly used progestins are medroxyprogesterone and norethindrone. There may be benefits in using actual progesterone rather than progestins. Progesterone is fairly well absorbed through the skin; some alternative practitioners have, for years, promoted the use of progesterone creams. Such progesterone creams are typically, but misleadingly, said to contain natural progesterone. This is an oddly chosen term, as the progesterone in these creams is actually produced in a laboratory, just like other synthetic hormones. To avoid confusion in this article, we will call progesterone true progesterone, or just progesterone. Besides creams, a special form of true progesterone that can be absorbed orally, micronized progesterone, has recently become available as a prescription drug. Progesterone cream appears to reduce menopausal symptoms. However, contrary to numerous misleading reports, it has not been found helpful for osteoporosis.

Progesterone is synthesized in the body and is not found in appreciable quantities in food. For use as a drug or dietary supplement, progesterone is synthesized from chemicals found in soy or Mexican yam. Note: Contrary to widespread misrepresentation, Mexican yam by itself contains no progesterone, nor any substance that the body can turn into progesterone.

The usual dose of progesterone in cream form is 20 mg daily. Although this dose may decrease menopausal hot flashes, even 3 to 4 times that amount does not provide enough progesterone to protect the uterus from the effects of estrogen. However, oral micronized progesterone taken at a dose of 200 to 400 mg daily should be approximately as effective as standard progestins.

Progesterone cream has been widely promoted as a treatment for osteoporosis, primarily by one author. However, the only meaningful study examining the issue failed to find progesterone cream effective for this purpose. In addition, oral micronized progesterone does not appear to add any additional bone-protective benefit in women taking estrogen. Like progestins, progesterone cream has been found effective in reducing menopausal symptoms. Also like progestins, oral progesterone protects the uterus from the stimulating effects of unopposed estrogen. This use requires physician supervision. Progesterone cream is probably not effective for this purpose.

Osteoporosis Despite widespread reporting that true progesterone is effective against osteoporosis, the best evidence we have is that it does not offer any such benefit. This notion began with test tube and other preliminary studies suggesting that progesterone or progestins can stimulate the activity of cells that build bone. Subsequently, a poorly designed and uncontrolled study (really, a series of case histories from one physicians practice) purportedly demonstrated that progesterone cream can slow or even reverse osteoporosis. However, a 1-year double-blind trial of 102 women given either progesterone cream (providing 20 mg progesterone daily) or placebo cream, along with calcium and multivitamins, found no evidence of any improvements in bone density attributable to progesterone. Furthermore, in a 3-year study of 875 women, combination treatment with estrogen and oral progesterone was no more effective for osteoporosis than estrogen alone. Menopausal Symptoms In the double-blind trial of 102 women described above, use of progesterone cream was, however, found to significantly reduce hot flashes and related symptoms.

Even though progesterone is sold as a dietary supplement, it is a hormone, not a food. We recommend that it not be used except under physician supervision. Like progestins, progesterone causes side effects. In one study, oral micronized progesterone at a dose of 400 mg per day was associated with dizziness, abdominal cramping, headache, breast pain, muscle pain, irritability, nausea, fatigue, diarrhea, and viral infections. Finally, women taking progestins to protect the uterus from the effects of estrogen should not substitute progesterone cream, because it is not sufficiently potent. Oral micronized progesterone, however, can be used for this purpose.