The best OTC cold medicine that works for me when I have a runny nose is Tylenol Cold + Head medicine.
It has always stopped my runny nose within about 30 minutes of taking the Tylenol Cold and Head medicine.
Staying hydrated and using a salt water saline solution to rinse your nasal passages out can also help stop a runny nose.
Most times runny noses happen due to irritants or inflammation of the nasal tissue but can also be because of a cold or flu.