To Your Health
Are bioidentical progesterone pills similar to the natural progresterone cream in the treatment of menopausal symptoms?
A. “Bioidentical” progesterone is produced in such a way as to have the same molecular shape and structure as the hormones made by your own body. Your body can use bioidentical progesterone as it was designed to, minimizing side effects. Almost all the molecules our bodies use have a distinctive shape, as a right-hand glove is different from a left-hand glove. Molecules as complex as hormones have many ways in which one can differ from another.
Synthetic progesterone, Provera for instance, is intentionally different from the hormone your body makes in order to be patentable. It will have somewhat of a different shape and different hormonal activity from the progesterone your body makes. A bioidentical hormone cannot be patented, so a drug company designs a synthetic molecule with appropriate hormonal activity that is patentable, and more profitable.
The bioidentical progesterone in the nonprescription topical cream that your friends use is the same as that in your prescription pills. However, the pills require roughly 10 times the dose as the cream to produce that same hormonal effect, 100-400 milligrams/day from the pills compared to 10-40 milligrams/day as cream. One reason is that absorption of progesterone from an oral dose is very poor compared to absorption through the skin.
Physicians, from years of experience, are most familiar with blood tests for hormone levels. Recently saliva hormone testing has become commercially available, and there are significant differences in the interpretation of results from the tests. In blood (or, more correctly, serum), hormones are combined with proteins in order to remain in solution and thus be transportable. While bound to protein, the hormones are not active. Although the blood test will report on the total amount of hormone in the blood, bound and free, only 5% or so is free and active. In contrast, all the hormones found in saliva are free, and the saliva hormone level reflects the active fraction of serum hormones. Physicians who are accustomed to interpreting serum hormone levels are required to adjust to different “normal ranges” in saliva.
In addition to getting used to different normal ranges, physicians who use saliva hormone testing have noticed another difference between the two test methods: when topical hormone creams are used, saliva hormone levels increase out of proportion to the dose. Serum hormones are not affected, but this has caused many women to stop using progesterone cream in spite of observed benefits. There is a technical explanation for the inordinate rise in saliva hormones when topical hormones are used, but for most people it is sufficient to simply divide the saliva hormone test results by 50 to arrive at a number that is comparable to the serum hormone number.
Bioidentical progesterone, although probably safer than synthetic progesterone, has not yet been well studied in long-term use. It should be considered a “naturally occurring drug” and no drug is completely safe. The dose of bioidentical progesterone needs to be matched to each woman’s needs, which is the purpose of the hormone tests.