Birth control... The pill

Michelle

My doctor put me on the pill, and told me to start it the first day of my period.

This never crossed my mind while I was in the office. I plan on taking the pill in the morning. It will be most convenient. The doc told me to start when It the first day of my period. Now how does this work if I start my period later in the day. Say around 9 or 10 at night.

I'm so new to this, and is there anything I should ask the pharmacist when I pick it up?