Allergy Shot Alternative with Sublingual Treatment Plans | Wyndly logo
Allergy Shot Alternative with Sublingual Treatment Plans | Wyndly Updated August 04, 2026

SLIT in the U.S.: FDA rules, 21 CFR 610.17, and the 2021 CBER letter (neutral overview)

How SLIT is regulated in the United States

Sublingual immunotherapy (SLIT) in the U.S. is regulated by FDA’s Center for Biologics Evaluation and Research (CBER). In practice, only a small set of SLIT tablets are FDA-licensed; physician‑compounded liquid “allergy drops” are used off‑label and are not FDA‑approved. The summary below maps what’s approved, what’s not, and why the March 23, 2021 CBER Untitled Letter to Curex matters for anyone communicating about SLIT.

What is FDA‑approved vs off‑label today

SLIT modality Allergens covered FDA status (U.S.) Age indication (as of Nov 13, 2025) Examples / labels
Tablet (dissolving under the tongue) Grass, ragweed, house dust mite FDA‑licensed biologics Grastek 5–65; Oralair 5–65; Ragwitek 5–65; Odactra 5–65 FDA pages for Grastek, Oralair, Ragwitek, Odactra; FDA tablet list overview
Liquid drops (custom mixtures) Often multiple aeroallergens (e.g., pollens, pet dander, molds, dust mites) Not FDA‑approved for SLIT use; off‑label use of licensed injectable extracts Determined by clinician; no FDA SLIT‑drop labeling Professional overviews noting drops are not FDA‑approved: ACAAI, Johns Hopkins Medicine

Notes:

  • FDA maintains product‑specific pages for each licensed tablet with current indications and ages (e.g., Odactra’s label updates through 2025 are listed on its FDA page). The FDA also maintains a consolidated list of all SLIT tablets.

  • Clinical societies and major centers state that liquid SLIT drops are not FDA‑approved; they are a physician‑directed, off‑label use of FDA‑licensed allergen extracts.

21 CFR 610.17: why mixtures matter

The eCFR provision 21 CFR 610.17 (“Permissible combinations”) states that licensed biological products “may not be combined with other licensed products … except as a license is obtained for the combined product.” In plain terms: combining licensed allergen extracts into a new mixture creates a new biologic that requires its own Biologics License Application (BLA) if it is to be marketed as a product. This rule underpins FDA’s repeated reminders that compounded mixtures of licensed allergenic extracts cannot be marketed as new products without an approved BLA.

March 23, 2021 CBER Untitled Letter to Curex (concise, dated summary)

  • Date and type: FDA/CBER Untitled Letter, March 23, 2021. PDF posted on FDA’s site: “March 23, 2021 Untitled Letter – Curex, Inc.”

  • What FDA reviewed: Curex’s website marketing of mixtures of allergenic extracts for sublingual immunotherapy (“allergy drops,” “drop compounds”).

  • Claims cited as examples (verbatim in the letter): “treats people who suffer from all types of allergies,” “equally effective,” “We use FDA‑approved extracts…,” and customization across multiple allergens.

  • Findings and legal bases:

  • FDA states the “allergy drops” and “drop compounds” are both drugs (FD&C Act §201(g)) and biological products (PHS Act §351(i)) and thus require a valid BLA or, during development, an IND.

  • FDA explicitly cites 21 CFR 610.17: mixtures of licensed allergenic extracts require their own BLA to be lawfully marketed.

  • FDA reiterates that biologics subject to §351 are not eligible for the compounded drug exemptions under FD&C Act §§503A/503B.

  • Response requirement: FDA requests a written response within 30 days of receipt, outlining corrective actions.

Reference: FDA/CBER Enforcement listings include the “March 23, 2021 Untitled Letter – Curex, Inc.” entry on the CBER enforcement page (BIMO/Internet Surveillance) with a direct link to the PDF.

What this means for compliant messaging (practical checklist)

Use the points below when describing SLIT, your services, or patient education. The goal is to be accurate, non‑misleading, and aligned to FDA’s frameworks.

Do say

  • “FDA‑approved SLIT tablets exist for grass (Timothy/cross‑reactive), short ragweed, and house dust mite.”

  • “Custom sublingual drops in the U.S. are an off‑label use of FDA‑licensed allergen extracts; they are not FDA‑approved for SLIT.” (Cite clinical society/major‑center pages above.)

  • “Compounded allergen mixtures are patient‑specific and not FDA‑approved products; 21 CFR 610.17 requires a BLA to market any new combined biologic.”

  • “Outcomes vary; most SLIT programs require months to years of consistent dosing for benefit.”

Avoid

  • “FDA‑approved allergy drops” (drops are not FDA‑approved for SLIT in the U.S.).

  • “Cure,” “permanent,” or “guaranteed” relief claims; instead, use “long‑term” or “durable” relief when supported by data and label.

  • “Treats all types of allergies” or blanket, non‑qualified efficacy statements for all allergens or populations.

  • Implying that mixed custom drops are FDA‑licensed or that compounding exemptions (503A/503B) authorize marketing of combined biologic “products.”

Related FDA and professional resources

  • FDA overview of Allergen Extract SLIT Tablets (list of approved tablets)

  • Product pages: Grastek, Oralair, Ragwitek, Odactra

  • 21 CFR 610.17 (Permissible combinations)

  • CBER Enforcement list entry and Curex Untitled Letter PDF

  • Clinical society/academic overviews clarifying tablet approvals vs drops: ACAAI, Johns Hopkins Medicine

Wyndly resources for further reading