Everyone is different, so I can't say what for who, but I've found everything to be pretty much placebo, with the exception of constantly sucking on lozenges that hurt my teeth, but at least lessen the soreness of my throat.
Cough syrups don't do anything really beyond a couple minutes of coating the throat.
These things have to work through your system and get out after a few days, there is no cure besides time. Drink a lot of water and tea to keep hydrated and somewhat warm and make sure you're not starving yourself.