Is it harmful to use nasal spray every night before bed?

My fiance always has a congested nose, even when he's not sick, and says his mouth is too dry in the morning if he doesn't use nasal spray at night (because he only breaths through his mouth at night). He is going to talk to his doctor about it soon, but in the meantime he uses nasal spray every single night before bed and has been for the last few months. Can this be harmful? Thanks