Earlier quoted context omitted.
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 C…
If we are talking about BNW, which was written in 1931, then that book predates benzodiazepines by 25 years or so. Perhaps you are thinking about barbiturates?
(By contrast, turns out 1984 -- which is always paired with BNW -- came out later than I thought, in '49. Yet BNW seemed more forward-looking. I always imagined it was written partially in response. It wasn't.)
There goes my benzo theory.
Though they remain what I imagine when I read about soma.