Melatonin is also the chemical produced by a human's body (and it's also available in pill form) used to make said person sleep, and the more produced, the faster they will fall asleep, and better they will sleep overall. [Click Here for more information]
The word "The" doesn't mean it occurs mostly in the "T" section; rather, it is excluded so that the next word after the word "The" (e.g.: "The Alchemist's Nightmare") will occur in that specific letter (e.g: "A").