As this Reactions video points out, most over-the-counter cough syrup does contain active ingredients (such as dextromethorphan (DMX) and guaifenesin) that are supposed to stave off coughs caused by illness or allergies. Well, at least in theory.
Trouble is, there’s a startling lack of scientific evidence to prove that cough syrup actually works. Studies show that these modern elixirs have virtually no measurable effect on coughs, and when not used properly, they can make you feel even sicker. In many cases, you’re just as well off sticking to grandma’s home remedy.