I don't know about prophylaxis, but I find 1 ZN (23 mg)/quercetin (800 mg) will dry up my stuffy head in about half an hour, better than Flonase or antihistamine because it even opens the Eustachian tubes. (prob. shouldn't use every day) Don't know which is the drying agent, but I suspect the ZN because I have seen it in a homeopathic compound called Sambucol "to take at first sign of a cold." It is also instant drying, but I like the quercetin better.