I've read there are pills to reduce seasonal allergies (sublingual immuno-therapy (slit), is this available yet, and why hasnt it replaced injections?

Need more studies: Slit at this time has not been approved by fda, no established standard dosing, may not work usa because most patients have more than one allergen (grass, dust, tree) that they are allergic to and slit studies usually were with patients who were only allergic to single allergen(grass only). The protection of slit still hasn't been completely studied. Injections is a better option at this point.