Starting on the pill.

Abstract
Starting the pill on the first day of a menstrual cycle, starting a new pill on the first day of a cycle, or starting a new pill the day after finishing the old pill eliminates the need for extra precaution contraceptives. A study of 567 women at the Oxfordshire Area Health Authority found that of the women using the first day cycle regimen, only 70 out of 353 reported spotting, amenorrhoea, or heavy period. 31 of 214 starting a new pill immediately after an old reported menstrual complaints. None became pregnant. Of 17 doctors asked their opinion of the new regimen 15 thought it worked well, particularly the immediate changeover routine. Patients liked the regimen because the lack of extra precautions makes it simple and economical.