it tells you the effects with the instructions. bleeding is one of them
I know this is an old post, but I wanted to reply because there may be other women out there that have googled "spotting before perion after Plan B" as I did. I NEVER spot before my period so I was convinced it had to be implantation bleeding when I started spotting scant amounts of light brown discharge 3 days before my period. I took Plan B after a condom broke during sex on my peak ovulation day. Pregnancy test was negative, but I thought it was too early.
My period came on time, exactly 28 days after the last one. I guess the spotting was either due to Plan B, or it was something new that I can expect to happen now.
Hope this provides some comfort to anyone reading this who is worried that spotting may be implantation bleeding.