The doctor's response: The answer to your question depends on when in your menstrual cycle you started taking the pill. If you started taking the pill within the first 5 days of your cycle (with day 0 being the day you would have expected to have your period), then your contraceptive is effective immediately. However, if you started taking the pill at any other time in your cycle, you should use a second form of contraception for 7 days to ensure your contraceptive is fully effective. If you are unsure of which day of your cycle you were on, it is best to use additional protection for 7 days, until next Monday. I hope this answers your question!