Definition
Therapeutic Equivalence Code (TE Code)
A Therapeutic Equivalence Code (TE code) is the rating the FDA assigns in the Orange Book to show whether a drug product is therapeutically equivalent to other pharmaceutically equivalent products, meaning it is expected to have the same clinical effect and safety profile.
2 min readReviewed September 14, 2026
Also known as: TE rating, AB rating, Orange Book rating, Therapeutic equivalence evaluation
Key facts
- Published in
- FDA Orange Book
- Format
- Two letters, sometimes followed by a number (AB1, AB2)
- A codes
- Therapeutically equivalent to other pharmaceutically equivalent products
- B codes
- Not considered therapeutically equivalent at this time
- Applies to
- Drugs approved under NDAs and ANDAs; not biologics
What is a therapeutic equivalence code?
The FDA considers two drug products therapeutically equivalent when they are pharmaceutical equivalents (same active ingredient, dosage form, route and strength) and can be expected to have the same clinical effect and safety profile under the conditions in their labeling. In practice that usually means the products have been shown to be bioequivalent.
TE codes are assigned to multisource products, where more than one pharmaceutically equivalent version is approved. A brand with no generic or other pharmaceutical equivalent is generally listed without a TE code.
Biologics do not receive TE codes. The closest concept for them is an FDA interchangeability determination, shown in the Purple Book.
How TE codes are structured
The first letter carries the main meaning, and the second letter adds detail:
- AA: conventional dosage forms with no known or suspected bioequivalence problems.
- AB: products that meet the necessary bioequivalence requirements, a rating widely seen on oral generics.
- AN, AO, AP and AT: A-rated aerosol nebulizer solutions, injectable oil solutions, injectable aqueous solutions and topical products.
- AB1, AB2 and similar: separate equivalence groups when a drug has more than one reference product and those references are not equivalent to each other.
- B codes such as BC, BD, BP and BX: products with actual or potential bioequivalence problems or insufficient data, which are not considered substitutable.
Why TE codes matter
State generic substitution laws decide what a pharmacist may substitute, and many rely on Orange Book A ratings. The FDA publishes the evaluations but does not itself regulate pharmacy substitution.
For analysts, TE codes define the real competitive set for a drug. Grouping NADAC prices or pharmacy claims by TE code and reference product separates truly substitutable generics from products that share an active ingredient but are B-rated or unrated, such as some extended-release reformulations.