How long should I keep using rhinolast nasal spray?

Seasonally. Are you taking it for seasonal allergies? If yes, take it as prescribed during seasons when you have allergies. You don't need to take it at times of year when you don't have allergy symptoms. Rhinolast controls allergy symptoms but it doesn't cure them so if you stop it during allergy season, your allergies will come back. If you have allergies all year round, you'll need to take it all year.