So the treatment of symptoms, in general, leads to some really inconsistent results, as it's really hard to measure them. Some studies have definitely found guaifenesin to not be helpful (others have), but the way all of them measure it is...questionable. Ultimately, what a user wants is a subjective experience of "I feel better", but what is being tested for is stuff like "what concentration of inhailed capsaicin leads to them coughing".

So generally my take is "hey, this is what it's been found effective for, and it's generally regarded as safe to take. Is it going to help here, for you, in this situation? Who knows! Give it a whirl if you got the money and want to try".

Guaifenesin is mostly useless and only approved so that they can stick it next to your dextromethorphan as an emetic to stop you from abusing it. I was vomiting from COVID and I was incredibly pissed off when I found out it was actually just because they poisoned my cough syrup on purpose.