How effective is taking plan b & taking your birth control pill the same day as taking plan b ? do they cancel each other out ?

Plan B: Depending on the kind of birth control pill, they contain similar hormones related to progesterone, levonorgestrel. It isn't necessary to take plan b if you haven't missed 2 or more birth control pills in a row. Plan B is 85% effective if taken within 72 hours and 95% effective within 24 hours, less effective in women with BMI's over 35.

They do not: cancel eath other out. However, if you are taking your normal birth control pill consistantly & correctly - than the Plan B is not needed.