34399,
I'm a doc, and rarely say forever for meds, without a good reason. I think your doctor is emphasizing that the kind of inhaled corticosteroid spray (probably Rhinalar, Flonase, Rhinacort or Nasacort), does not fix things quickly. It takes a few weeks for any effect on hay fever, and much longer for polyps. I think you are reasonable in your thoughts of trying for 6 months or a year, then using antihistamines intermittently after this...
If the problems persist, you may indeed be on these for life.
Very little of these inhaled nasal "steroids" are absorbed into the rest of your system, so the systemic side effects are non-existent, as much as we can ever say this...Neemer (a pharmacist) may have figures on the systemic effects.
cheers
ozball