Fertility control by cyclic norethindrone administration was studied in 364 women over a period of 32 months, for a total of 6,062 cycles. The agent was effective, harmless, and more acceptable than any other method available. Subsequent fertility was unimpaired. There were additional desirable effects, including regularization and diminution of menstrual flow and decrease of dysmenorrhea.
Rice-Wray E, Schulz-Contreras M, Guerrero I, Aranda-Rosell A. Long-Term Administration of Norethindrone in Fertility Control. JAMA. 1962;180(5):355–358. doi:10.1001/jama.1962.03050180001001