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.