I think he was inspired by Valium and other benzos. They put people into a docile, low-anxiety state, and they were popular around the time the book was written.

That's also more-or-less consistent with the implied literary reference to the Lotus Eaters, who I think are usually imagined as opium users. Opioids are different but are also downers that reduce anxiety.

Benzos later featured significantly in one of Adam Curtis' film-essays -- maybe Century of the Self, maybe another one. I'd view those films as being in a similar spirit to Brave New World.