The term "narcotic" actually has a bit of a gray meaning. To the Jem'Hadar, I suppose it would be a narcotic, but it is not a drug that is of any use to anyone else. It's made up of an isogenic enzyme which means that it is specifically, genetically structured for the Jem'Hadar. It's an enzyme that their bodies require but do not produce as a means for control.
I think the term "narcotic" was used in Insurrection and that's where Memory Alpha got it. However, I don't think Michael Piller knew enough about it's properties or even put a lot of thought into the line when writing it. He just wanted to make the Son'a sound really bad and add in a nod to DS9. It's also easier in a movie where people may not be familiar with DS9 to use the word "narcotic" rather than "isogenic enzyme that the Jem'Hadar are addicted to."