Way, way back a few jobs ago, I worked for the company that developed Dextromethorphan. It's in just about every cough medication, cause it works. My group helped that production department solve a problem they were having with the process, which was decades old even then, back in the late 80s. There was a push for a while to move those meds behind the counter since people were using dextromethorphan to do some mind altering stuff, but the dosage would end up being so excessive, it never gained traction, so it's still out in the isles.
Look for that as an active ingredient if you have a cough that won't go away, it won't cure the illness, but it'll make that symptom stop for a while.