Dexedrine

I drank gin-and-hot-water to blunt the pain and took Dexedrine to blunt the gin and wrote the piece.

Source: wiktionary

[…]—and then all soaring on—what?—acid, peyote, morning-glory seeds, which were very hell to choke down, billions of bilious seeds mulching out into sodden dandelions in your belly, bloated—but soaring!—or IT-290, or dexedrine, benzedrine, methedrine— Speed!—or speed and grass—[…]

Source: wiktionary

Later I learned that the pills were Dexedrine, which Elvis had first discovered in the Army. A sergeant had given several men pills to help them stay awake while on guard duty.

Source: wiktionary