I agree with the consensus here- you are thinking about this wrong. Allegra-D, the one behind the counter in my state, is an allergy medicine we use for colds, because it works better than anything labeled as cold medicine.

If you are saying you want something that treats allergies, and by treating them unstuffs your nose, that Allegra-D will work. I don’t understand why you think it won’t. The pseudoephedrine in it (the D in the name) is a vasoconstrictor that will open your nose.

If it’s the same drug labeled as a cold medicine, it would work exactly the same.