Guafenisin is pretty tolerable, IME.
They used to make this cough syrup, Codiclear DH, I believe it was. Stuff had nothing but Hydrocodone & guafenisin in a GREAT ratio, and it was clear, and tasted like bubble gum. Needless to say, I was niave at the time, and never threw up off it, not once, even after going through dozens of bottles.
Man I would give my left nut for a few 5-gallon buckets of that stuff!! The taste alone....chemically bubblegum elixir of the Gods, it was.