It’s important to understand that the antigens used in allergy drops are the same FDA-approved antigens used in allergy shots. They’re also prepared in the same way as allergy shots. The difference is the route of delivery — a dispenser that delivers a precise dose of antigen under the tongue versus a syringe injecting antigen into tissue.
The FDA approves products, not therapies, so it’s unlikely that it will ever “approve” custom, multi-antigen sublingual immunotherapy.
Antigens are labeled by the FDA for single use through injections and some for sublingual immunotherapy. Multiple antigen therapies for both injection and sublingual use are an off-label use of FDA-approved biologics.
Most physicians prescribe FDA-approved drugs in an off-label manner today, for example, the use of blood pressure medications for migraines, montelukasts for COPD, or arthritis drugs to treat shingles.