Progestins

Progestins are synthetic drugs that act like the body's own progesterone. They bind to the same cell receptors (progesterone receptors). They can change the endometrium, the lining of the uterus. They can relax the muscle of the uterus. They also send signals to the brain that shape the menstrual cycle. Progestins differ from bioidentical progesterone, which matches the body's own hormone. Their structure is different. The body breaks them down in a different way. Their side effects also differ.

Progestins come from two main families. Some are made from testosterone, such as norethindrone, levonorgestrel, and desogestrel. Others are made from progesterone, such as medroxyprogesterone acetate. Drospirenone comes from a third family, related to the diuretic (water pill) spironolactone.¹ Many progestins also act on other hormone receptors in the body. Some act like male hormones. Some block male hormones. Others act like stress or salt-balance hormones. These added effects vary from one drug to the next. Progestins are the active drug in many suppressive medications. These include the combined pill, the progestin-only pill, hormonal IUDs, the implant, and the Depo injection. Some menopause hormone regimens use them as well.

Restorative Reproductive Medicine draws a clear line between progestins and bioidentical progesterone. NaProTechnology terminology, developed by Dr. Thomas W. Hilgers, classifies progesterone as an isomolecular hormone. It classifies progestins as heteromolecular "artimones." NaProTechnology clinicians use bioidentical progesterone for luteal phase defect, a weak second half of the cycle. They also use it for threatened miscarriage and premenstrual symptoms. They choose it because the two differ in their action on cells, in breast safety, and in pregnancy safety data. The form and route are chosen for each person.