[header] How to stop a cough from post nasal drip [title] Take mucus-thinning medications. [step] Mucus-thinning medications are also known as expectorant medications. This sort of medication causes the mucus to become thin and move up from your throat and into your mouth (you can then spit it out). 
It increases the amount of mucus you have, but thins it out so that your body-in particular the ciliated hairs in your throat-have an easier time getting out of your throat. When the mucus is removed, your cough will stop.