I watched ST Insurrection the other day an in the part where Riker and Troi are talking about the Sona (sp?) they say something about them selling or manufacturing Ketracel White. So do they use it or was it made for the Dominion?
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."
Kind of... except the Jem'Hadar go through withdraws similar to being taken off of an addictive drug. It's also very difficult to synthesize and also contains all the nutrients the Jem'Hadar need as an added bonus.
It actually makes sense for the Dominion to go to the Son'a to make white for them. After they were cut off from the Gamma Quadrant, they had to get it from somewhere. The Jem'Hadar are warriors, not manufacturers... and it isn't a good idea to trust them with the formula to the drug you are controlling them with. It seems unlikely that there were enough Vorta. They certainly didn't trust the Cardassians (and with good reason). So why not go through someone that had no vested interest in the war other than profit?