Ketracel-white, or simply white, was an isogenic enzyme, the ingredients of which included yridium bicantizine. The Jem'Hadar soldiers of the Dominion were genetically engineered to lack the enzyme which white provided, 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. (DS9 episodes: "The Abandoned", "Hippocratic Oath", "Statistical Probabilities")
Without white, Jem'Hadar soldiers would suffer withdrawal symptoms including pain, anxiety, loss of mental control, and inability to shroud; eventually the Jem'Hadar would become insane and kill everything they could, including each other, before their entire genetic structure collapsed. DS9 episodes: "Rocks and Shoals", "Behind the Lines")
The addiction to white also ensured the Jem'Hadars' loyalty to the Founders. (However, for most Jem'Hadar this is unnecessary, as their loyalty was already absolute.) Distribution of the white was controlled by the Vorta, and was dispensed to the Jem'Hadar First in a formal ceremony. ( DS9 episode: "To the Death")
- Vorta: "First, 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, due to the minefield blocking supplies from the Gamma Quadrant, and because it was not easy to set on new production lines. The Cardassians proposed exterminating some or all of the Jem'Hadar by poisoning the last white supplies. Later, the Son'a used facilities on Devos II to produce large quantities of ketracel-white. (DS9 episode: "Penumbra", Star Trek: Insurrection)
On rare occasions, a Jem'Hadar was born with a genetic mutation which allowed their bodies to produce the white they need, though such instances could go unnoticed. The first Jem'Hadar with this condition known to the Federation was Goran'agar. Following the Dominion War Odo searched for Jem'Hadar with the mutation, eventually finding the Jem'Hadar elder Taran'atar who he sent as an envoy to the Alpha Quadrant. (DS9 episode: "Hippocratic Oath"; DS9 - Avatar novels: Book One, Book Two)
Starfleet autopsies also led them to believe that some older Jem'Hadar, over ten years old, sometimes developed the mutation to produce white, in small quantities, themselves, as they aged. (DS9 - Avatar novel: Book Two)