Ketracel-white

Ketracel-white (or simply white) is an addictive substance containing an isogenic enzyme and nutrients. One of the active ingredients of white is yridium bicantizine. The Jem'Hadar soldiers of the Dominion are genetically engineered to lack the enzyme which white provides, and require frequent doses of the drug to survive. The white also provides all the nutrients they require, alleviating them of the need to eat or drink.

Without white, Jem'Hadar soldiers suffer withdrawal symptoms including pain, anxiety, loss of mental control, and inability to 'shroud'; eventually the Jem'Hadar will become insane and kill everything they can, including each other. Finally, their entire genetic structure will collapse. On rare occasions, a Jem'Hadar is born with a genetic mutation which allows their bodies to produce the white they need, though most such instances go unnoticed. (see also: Goran'Agar and Taran'atar) All attempts to medically cure the Jem'Hadar of their addiction have thus far failed.

The addiction to white ensures the Jem'Hadars' loyalty to the Founders. However, for most Jem'Hadar this is unnecessary, as their loyalty is already absolute. Distribution of the white is controlled by the Vorta, and is dispensed to the Jem'Hadar First in a formal ceremony:

Vorta: "First [name], can you vouch for the loyalty of your men?" Jem'Hadar: "We pledge our loyalty to the Founders, from now until death." Vorta: "Then receive this reward from the Founders, may it keep you strong." Early in the Dominion War, the Dominion in the Alpha Quadrant suffered of a White shortage, because the minefield prevented supplies from the Gamma Quadrant, and because it was not easy to set on new production lines. The Cardassians proposed to exterminate some or all Jem'hadar by poisoning the last White supplies. Later, the Son'a used their facilities on Devos II to produce large quantities of ketracel-white.

Presumably, the Dominion "subcontracted" White production to the Son'a because of the shortage. Given the repeated White supply problem, it is safe to assume that Ketracel can't be replicated, which further ensures the Jem'hadar's loyalty. See also: "The Abandoned" (DS9).