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Progesterone; Natural Progesterone; Micronized Progesterone; Progesterone Cream

Proposed Uses
  • ORAL:  Replacement for Standard Progestins
Other Proposed Uses
  • TOPICAL:  Menopausal Symptoms
Probably Not Effective Uses
  • TOPICAL:  Preventing or Treating Osteoporosis; “Opposing” Estrogen

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. However, it has been suggested that actual progesterone may offer benefits over progestins, such as fewer side effects.

Progesterone can be absorbed through the skin to some extent, and 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.
Inconsistent evidence suggests that progesterone cream might help reduce menopausal symptoms. However, it does not appear to be strong enough to balance the effects of estrogen, thus reducing the risk of uterine cancer. (Oral micronized progesterone is strong enough for this purpose.) Contrary to numerous books and magazine articles, there is no more than weak, inconsistent evidence that progesterone cream offers any benefits for osteoporosis.

Requirements/Sources
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: Another aspect of the widespread misinformation involving progesterone cream is the concept that Mexican yam itself contains progesterone, or substances that the body can convert into progesterone. This is incorrect. Industrial chemists can convert a constituent of Mexican yam (diosgenin) into progesterone, but only by using chemical pathways not found in the body.

Therapeutic Dosages
The usual dose of progesterone in cream form is 20 mg daily. Although this dose might decrease menopausal hot flashes , most studies found that even doses as high as 64 mg daily do not provide enough progesterone to protect the uterus from the effects of estrogen. However, one study found that use of micronized progesterone cream at 80mg daily produced similar progesterone levels in the body as an oral dose of 200mg daily; oral micronized progesterone taken at a dose of 200 to 400 mg daily is approximately as effective as the standard dosage of the more commonly used progestins.

Therapeutic Uses
Progesterone cream was widely promoted in the 1990s a treatment for osteoporosis, on the basis of meaningless “studies” whose design was too poor to establish anything at at all. When properly designed studies were performed, the results were at best inconsistent.

Studies conflict on whether progesterone cream can help hot flashes. One double-blind, placebo-controlled study failed to find any improvements in mood or general well-being in menopausal women using progesterone cream.

Like progestins, oral progesterone protects the uterus from the stimulating effects of unopposed estrogen. However, standard doses of progesterone cream probably provide too little progesterone to serve for this purpose (see next section).

Safety Issues
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, true 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.

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