Contrary to popular belief, Phenylephrine which is in most cold medicines, does not work any better than placebos.

See: https://en.wikipedia.org/wiki/Phenylephrine

However, what actually works is Pseudoephedrine:
See: https://en.wikipedia.org/wiki/Pseudoephedrine

For coughs, the following works:
https://en.wikipedia.org/wiki/Acetylcysteine