When the past informs our future.

The continuous-use combination oral contraceptive ethinylestradiol/levonorgestrel 20microg/90microg suppresses gonadotropins, and subsequently ovulation and endometrial thickening, and suppresses breakthrough bleeding. Amenorrhoea and absence of breakthrough bleeding increase in incidence with extended administration. The pregnancy rate attributable to method failure in a large noncomparative trial of healthy, sexually active (aged 18-49 years) women during treatment with ethinylestradiol/levonorgestrel 20microg/90microg for 12 months was 15 per 2134 women (adjusted Pearl Index 1.26 per 100 women-years of use). There were no differences in pregnancy rates over 12 months between continuous-use ethinylestradiol/levonorgestrel 20microg/90microg and cyclical ethinylestradiol/levonorgestrel 20microg/100microg in a smaller, randomised, nonblind trial. Adverse menstrual cycle-related symptoms were significantly improved with administration of continuous-use ethinylestradiol/levonorgestrel 20microg/90microg in a noncomparative trial. In small trials, hormonal and ultrasound changes indicative of reinstated ovulation occurred within a month of discontinuation of the drug, and menstruation began again in most women within 90 days. The incidence of adverse effects was similar in continuous-use and cyclical regimens of ethinylestradiol/levonorgestrel (20microg/90microg vs 20microg/100microg).