I'm with leighsa200. PE is junk. Go to the pharma counter and ask for the real stuff. They keep it back there because nefarious types can manipulate the ingredients to make crystal meth, so that's why they're checking IRAB. Still, nothing compares to the real thing and it's worth the trouble.
To answer your question, I believe I have taken 2 PE's when the first didn't work. Don't remeraber the second making a difference though.