From Furukawa, C. T., & Lodewick, M. J. (2007). β-adrenergic agonists. In Allergic Diseases (pp. 335-342). Humana Press.:
Epinephrine has both α- and β-adrenergic actions, which make it the drug of choice
for the treatment of anaphylaxis. It is effective as an injection, but not orally, because
epinephrine and other catecholamines are rapidly inactivated by the action of catechol O-methyltransferase (COMT), an enzyme present in the gastrointestinal wall
So, it's not effective to give orally because it breaks down in the GI tract and isn't effectively absorbed. I'd also add that it's not really an anti-allergy medicine but rather for specifically treating anaphylaxis, and it also is not great for anything besides emergencies because it has a lot of (especially cardiovascular) side effects and has a short half-life.