Norethisterone acetate (abbreviated as NETA), or norethindrone acetate, is a progestin which is used in hormone replacement therapy, and to treat gynecological disorders, especially adenomyosis (the inner lining of the uterus breaks through the muscle wall of the uterus) and endometriosis (endometrial cells are found growing outside of the uterus). NETA is also used as a hormonal contraceptive in combination with estrogen, in the treatment of gynecological disorders such as abnormal uterine bleeding.

It causes a hypoestrogenism (low level of estrogen in bloodstream) by suppressing hormones that stimulate the gonads, or sex glands, to carry out their reproductive or endocrine functions), inhibiting ovulation, and developing amenorrhea (the absence of a menstrual period in a woman of reproductive age) with eventual partial or complete wasting of inner layer of the uterus (endometrial atrophy).

NETA is a prodrug of norethisterone in the body.Upon oral ingestion, it is rapidly converted into norethisterone by esterases during intestinal and first-pass hepatic metabolism. Hence, as a prodrug of norethisterone, NETA has essentially the same effects, acting as a potent progestogen with additional weak androgenic and estrogenic activity.

Norethisterone acetate offers various advantages for the long-term treatment of endometriosis. Early studies showed that NETA was effective in reducing chronic pelvic pain in women with laparoscopically confirmed endometriosis. It allows good control of uterine bleeding; it has positive effect on calcium metabolism and no negative effects on the lipoprotein metabolism at low dosages.

In women with rectovaginal lesions or colorectal endometriosis, NETA at low dosage should be preferred.

  • thrombophlebitis ( vein inflammation related to a blood clot)
  • cerebral thrombosis and embolism (a blood clot in the brain)
  • hypertension (high blood pressure)
  • edema
  • depression
  • changes in libido
  • changes in appetite
  • headache
  • nervousness
  • dizziness
  • fatigue
  • allergic rash
  • melasma (a condition which causes dark, discolored patches on the skin) 
  • hirsutism (when a woman has excessive hair growth)
  • alopecia (a condition in which hair is lost from some or all areas of the body)
  • erythema multiforme (a skin reaction that can be triggered by an infection or medication)
  • erythema nodosum (inflammation of the fat cells under the skin, resulting in tender red nodules or lumps that are usually seen on both shins)
  • itching
  • neuro-ocular lesions (eg. retinal thrombosis)
  • breakthrough bleeding
  • spotting
  • amenorrhea
  • increased cervical erosion and secretion
  • cystitis (an inflammation of the bladder)
  • cholestatic jaundice (a condition where bile cannot flow from the liver to the duodenum)
  • weight gain and loss
  • pulmonary embolism (a blood clot in the lungs)
  • premenstrual syndrome
  • backache

NETA has been reported to be effective in the treatment of endometriosis. NETA as a medical management of adenomyosis is a novel therapy. However, significant breakthrough bleeding is reported in patients of endometriosis being treated continuously with NETA.

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