How long does it take for birth control to be effective once you start taking it?

im starting yaz does anyone have any info they feel i should know.How long does it take for birth control to be effective once you start taking it?
My doctor recommended that I use protection until I completed my first 28 days of using the pill.How long does it take for birth control to be effective once you start taking it?
a full cycle of the pills (ie 28 days, including the 7 days of sugar pills)
It should take 7 days for you to be covered...I'd advise not totally relying on it thought because there could still be other things which can stop its effectiveness i.e the runs, being sick, stress etc. Also, dont eat grapefruit when on most pills as it reduces the effectiveness. Not too sure if this is the same when on Yasmin though.