Primolut N (norethisterone) is an oral hormonal contraceptive, a form of progestin manufactured by Bayer, that has been used as a contraceptive since the 1970s.

It is also used to treat endometriosis and dysmenorrhea (painful periods).

How Primolut N works

During each menstrual cycle, the inner lining of the uterus — called the endometrium — swells and sheds in response to hormonal cycles. The female hormone progesterone is required to maintain the endometrium, and its levels go down during menstruation to enable the shedding of the endometrial tissue.

Endometriosis is a condition characterized by the growth of endometrial-like tissue outside the uterus. Since there is no safe passage for this extra-uterine endometrial tissue to leave the body, patients experience severe pain when it too breaks down as part of the monthly cycle.

Primolut N is a progestin (a synthetic form of progesterone) that is very similar to the naturally occurring hormone. During the secretory phase of the menstrual cycle (days 14 to 28), the endometrium matures under the influence of progesterone.

By mimicking the function of progesterone, Primolut N prevents the shedding of the endometrium. For some patients, this helps to reduce the pain and inflammation associated with endometriosis.

Primolut N in clinical trials

There have been many clinical trials to assess the safety and efficacy of Primolut N in endometriosis.

For example, a Phase 3 randomized clinical trial (NCT00212342) assessing the effect of a combined oral contraceptive (COC) consisting of norethisterone (the active ingredient of Primolut N) and ethinyl estradiol in treating dysmenorrhea was completed in 2006.

Primolut N was also co-administered along with the steroid sulfatase inhibitor PGL2001 in a Phase 2 multicenter and randomized clinical trial (NCT01631981) to check for efficacy in treating pain symptoms associated with endometriosis.  

The effect of a combination of norethindrone acetate and estradiol along with the gonadotropin-releasing hormone (GnRH) receptor antagonist Relugolix is currently being evaluated in three Phase 3 clinical trials — SPIRIT 1 (NCT03204318), SPIRIT 2 (NCT03204331), and SPIRIT Extension (NCT03654274) — as a potential treatment of endometriosis-related pain.

Other information

For endometriosis, Primolut N is usually taken twice daily between the first and fifth day of the menstrual cycle. The dosage may be increased in the event of spotting (bleeding outside normal periods). Continued use of Primolut N prevents ovulation and menstruation from occurring, but bleeding will resume after withdrawal from the treatment.

Primolut N should not be used when pregnancy is confirmed or suspected and during lactation. It is also not advisable to take Primolut N if there is a presence or history of venous or arterial thromboembolic conditions where clots form inside blood vessels.


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