Such a large subject that i feel it would be better if your Googled hay fever and it's treatment.
However, here are my feelings on the subject.
If the symptoms are mild then over the counter medication by anthistamines either by mouth or by sprays should suffice.
Where these treatments are ineffective, regular intranasal
corticosteroids should be used. Intranasal steroids are more effective if used at the start of the season and in the presence of established nasal congestion, a topical decongestant may be used for up to one week as a pre-treatment.
If all these methods fail or if it is for a special occasion e,g exams, wedding then a short course of steroids by mouth are =, in my opinion justifiable.
Injectable steroids seem to be a contentious issue in the UK and many other countries,but should not be discounted.
Treatment of hay fever is b y trial and error.