FWIW, I'm sick and am currently looking at a bottle of Robitussin Dry Cough Forte, and the only active ingredients are DXM. But yes, if you're wanting to do high doses, tablets are gonna be the least unpleasant option
That's because, as far as it exists, America's nanny-state sucks, (the secondary drug ingredients have a dual purpose of treating some other ailment beyond cough, such as chest congestion, and dissuading from intentional medicative overdose), and you're probably D&U.
Agreed on the nanny-state bit, but we kind of get what we deserve since most people are ok with "protecting" us from dangerous drugs. Except for alcohol and tobacco, those get a pass for $ome rea$on.
At least cannabis is making it's way into normality and states are recognizing that there's money to be made.