Bio-identical (sometimes called natural) hormones are chemically and biologically identical to the ones produced by the human body. The molecular structure of the hormone is exactly the same and they effect the same physiologic function in the body.

Synthetic hormones, on the other hand are chemically similar but not identical and do not completely match the receptor sites for which hormones were designed. These hormones have chemical side chains added to their molecular structure which may be the cause of deleterious side effects.

Bio-identical hormones are chemically derived from plant sources (soybean or Mexican wild yam) and have a very short half life (do not remain in the body for very long). While they are derived from plant sources they consist only of the pure hormone and do not contain any traces of the plant from which it was sourced.

Everyone has a different reason for using hormone replacement. Some people want to alleviate symptoms caused by the decrease in the body's production as aging occurs. Others want to confer the protective benefits on the body originally provided by their naturally occurring hormones. In re-establishing hormonal balance it seems intuitive to use the same compounds for which the body's receptor sites were designed.

Synthetic hormones have quite a long half life and can be present in the body for days to months after discontinuation. The metabolites formed by the body's efforts to eliminate synthetics are often what cause patients to experience side effects.

This is the 5-10 years leading up to menopause (cessation of menses) during which time women may experience a host of symptoms from hot flashes and night sweats to irregular or heavy periods, loss of sex drive, thinning hair, insomnia, memory lapses, and depression.

This term applies to women who have not experienced a period for one year. From this time forward she may begin to experience symptoms of rapid aging, thinning skin, vaginal dryness, osteoporosis, and functional hypothyroidism.

While some women do fine after hysterectomy the surgical procedure itself may induce an early menopause by interrupting blood supply to the ovaries, the primary source of her hormones. Oophorectomy, the surgical excision of the ovaries, will invariably result in sudden and marked changes in a woman's body. These women almost always require some hormone intervention to alleviate symptoms and restore their body's physiologic well-being.

Women who have put off their pregnancies until their late thirties (or those who have continually suppressed their hormone production through use of birth control pills) often find they have insufficient endogenous hormones to sustain a pregnancy. In addition, continuous use of birth control may have caused them to become functionally hypothyroid.

Males often experience a decline in androgen hormone levels characterized by loss of energy, sex drive, physical strength and abdominal weight gain. This change is sometimes referred to as "Andropause"  and is not as predictable as the female "Menopause". It is the unpredictability that may cause this change in a man's body to go unrecognized until it suddenly hits him like a ton of bricks.