Norethindrone acetate 1.0 milligram and ethinyl estradiol 10 micrograms as an ultra low-dose oral contraceptive

Obstet Gynecol. 2013 Sep;122(3):601-7. doi: 10.1097/AOG.0b013e3182a1741c.


Objective: To assess the efficacy, safety, and tolerability of an extended-duration, combined hormonal oral contraceptive pill (OCP) that reduces the estrogen exposure by almost half compared with other OCPs.

Methods: This open-label, uncontrolled, multicenter study used an ultra low-dose OCP (1.0 mg norethindrone acetate and 10 micrograms ethinyl E2). The OCP was administered in a regimen of 24 days of a 28-day cycle followed by 10 micrograms ethinyl E2 for 2 days and an inactive tablet for 2 days. The study included healthy, heterosexually active women aged 18-45 years who were at risk of pregnancy.

Results: The discontinuation rate was 41.7% (692/1,660 patients). Twenty-six pregnancies occurred in 1,555 participants during 15,596 at-risk cycles, resulting in a Pearl Index of 2.2 and a cumulative pregnancy rate of 2.1 for the overall population. Participants experienced an average of 2.6 days of intracyclic (unscheduled) bleeding or spotting per cycle over treatment cycles 213. Intracyclic bleeding was more common in users new to OCPs than in users switching from another OCP and in women aged 18-35 years compared with those aged 36 years or older. The frequency of bleeding episodes decreased after cycle 2 and throughout treatment in all subpopulations.

Conclusion: The findings of this study demonstrate that this ultra low-dose OCP regimen is effective in preventing pregnancy with a safety and tolerability profile that is comparable with that reported for other low-dose OCPs.

Clinical trial registration:,, NCT00391807.

Level of evidence: III.

Publication types

  • Clinical Trial, Phase III
  • Multicenter Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Contraceptives, Oral, Synthetic / administration & dosage*
  • Contraceptives, Oral, Synthetic / adverse effects
  • Ethinyl Estradiol / administration & dosage*
  • Ethinyl Estradiol / adverse effects
  • Female
  • Humans
  • Menstruation Disturbances / chemically induced
  • Middle Aged
  • Norethindrone / administration & dosage
  • Norethindrone / adverse effects
  • Norethindrone / analogs & derivatives*
  • Norethindrone Acetate
  • Pregnancy
  • Pregnancy Rate
  • Young Adult


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

Associated data