Question: I was wondering about the title change from "Leon" to the "Professional". Was the title only changed in the U.S. and if so why?
Answer: According to IMDb.com the title was only changed in the United States and the reason why was maybe audiences would find the title, "The Professional" more appealing than "Leon."
Question: Near the half-hour mark, Gary Oldman pulls out a small box of green-and-yellow pills and takes one. What exactly is it?
Answer: Some kind of (unnamed) drug. Just to show how nasty the DEA agent is.
Answer: No specific reason is given; it's most likely intended to highlight that her family are bad people (they are drug dealers after all) and to show in contrast that Mathilda and her little brother are not, so we feel badly for them.
Purple_Girl