This female sex hormone is produced in the second half of the menstrual cycle (after ovulation) by the corpus luteum in the ovary. It prepares the uterus to receive a fertilized egg by stimulating the growth, blood supply and secretions of the endometrial cells of the uterus, and stimulates the mammary glands. Progesterone also stimulates the reabsorption of water, sodium and chloride ions by the kidneys, and this effect may be experienced as premenstrual fluid retention.

Some disorders of female health are attributed to an 'oestrogen overload' or to a progesterone deficiency, and there is an increasing tendency in the natural health movement to recommend rub-on progesterone creams to women with problems such as premenstrual syndrome, menopausal problems and osteoporosis. While this allopathic approach (similar to the use of oestrogen hormone replacement therapy) would never be tolerated if these creams were sold by the pharmaceutical industry, many practitioners have been persuaded that they are 'natural' because the raw material is extracted from plants. However, there is nothing natural about rub-on hormone treatments. Progesterone is secreted by the female body as and when it is needed, not on a permanent basis. The progesterone in such creams may take some months to permeate the body fat and to penetrate from here into the bloodstream. The long-term effects of saturating the body fat with these hormone treatments are unknown, but one likely effect is the development of a dependency state, as with artificial HRT. Hormone treatments suppress the body's own natural hormone production. Discontinuing the medication can lead to withdrawal symptoms which are identical to the original symptoms for which the medication was prescribed, but more severe. These makes the patient reluctant ever to discontinue the treatment and she may require higher and higher doses to maintain a feeling of well-being.

Oestrogen overload and progesterone deficiency problems are best treated by investigating their causes (such as poor liver clearance of oestrogen) and correcting any nutritional deficiencies such as iodine, zinc and vitamin E. Soya products can be powerful oestrogen balancers, and many herbal combinations such as those containing Agnus castus and dong quai also have a beneficial balancing effect on female hormones.