Efficacy and safety of a new 24-day oral contraceptive regimen of norethindrone acetate 1 mg/ethinyl estradiol 20 micro g (Loestrin 24 Fe)

Contraception. 2007 Jan;75(1):16-22. doi: 10.1016/j.contraception.2006.08.004. Epub 2006 Sep 20.


Background: New low-dose formulations of combination oral contraceptives (COCs) are safe and effective, but they may be associated with an increased risk of breakthrough bleeding. Extending the duration of active hormonal treatment may reduce the frequency of intracyclic bleeding/spotting while maintaining efficacy and tolerability.

Methods: This 6-month, open-label, randomized, active-controlled study involved healthy women aged 18-45 years who were at risk for pregnancy. Women were randomized 4:1 to a 24-day regimen of norethindrone acetate 1 mg/ethinyl estradiol 20 micro g (NETA/EE-24) or to a 21-day regimen of the same combination (NETA/EE-21). The outcomes assessed included pregnancy and incidence, duration of bleeding and intensity of bleeding.

Results: The cumulative risk of pregnancy in the NETA/EE-24 group (n=705) was 0.9% during six cycles of treatment. Compared with NETA/EE-21 (n=181), NETA/EE-24 was associated with significantly fewer intracyclic bleeding days (0.95 vs. 1.63; p=.005), fewer days of withdrawal bleeding (2.66 vs. 3.88; p<.001) and fewer total bleeding/spotting days for Cycles 2-6 (18.6 vs. 23.2; p<.001). NETA/EE-24 was well tolerated, and side effects were generally mild to moderate in severity.

Conclusions: NETA/EE-24 is an effective well-tolerated COC that is associated with a bleeding profile more favorable than that of NETA/EE-21.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Adolescent
  • Adult
  • Contraceptives, Oral, Combined / adverse effects
  • Contraceptives, Oral, Combined / therapeutic use*
  • Contraceptives, Oral, Synthetic / adverse effects
  • Contraceptives, Oral, Synthetic / therapeutic use*
  • Dose-Response Relationship, Drug
  • Estradiol / adverse effects
  • Estradiol / therapeutic use*
  • Female
  • Humans
  • Menstrual Cycle / drug effects
  • Menstrual Cycle / physiology
  • Metrorrhagia / chemically induced*
  • Metrorrhagia / epidemiology
  • Middle Aged
  • Norethindrone / adverse effects
  • Norethindrone / analogs & derivatives*
  • Norethindrone / therapeutic use
  • Norethindrone Acetate
  • Pregnancy
  • Pregnancy Rate*
  • Risk Assessment
  • Safety
  • Time Factors
  • Treatment Outcome


  • Contraceptives, Oral, Combined
  • Contraceptives, Oral, Synthetic
  • Estradiol
  • Norethindrone Acetate
  • Norethindrone