What are the Orange Book and Purple Book?
In the US, both “books” are drug reference databases maintained by the FDA, but they serve different purposes and cover different kinds of products.
Orange Book (FDA’s Approved Drug Products with Therapeutic Equivalence Evaluations) lists approved prescription drug products and assigns therapeutic equivalence ratings for generic vs. brand-name drugs (often used to support substitution and prescriber decisions). It’s the main reference many people use when asking whether a generic is considered equivalent to a brand. [1]
Purple Book (FDA’s Drugs@FDA: Drug Products, Including Biological Products With Therapeutic Equivalence Evaluations) focuses on biological products and also includes therapeutic equivalence information, but for biosimilars vs. reference biologics (and related biologic products). [2]
What’s the main difference: generics vs. biosimilars?
The clearest way to think about the two is:
- Orange Book = small-molecule drugs and generics (therapeutic equivalence ratings support generic substitution concepts). [1]
- Purple Book = biological products and biosimilars (therapeutic equivalence information is used for biosimilar/reference comparisons). [2]
Because biologicals are more complex than small-molecule drugs, the US uses different approval pathways and substitution frameworks, which is one reason the FDA maintains separate databases.
What does each book list (and what you’ll look for)
Orange Book commonly helps you find:
- Approved drug products (including generic applications)
- Active ingredients/strength/route/form
- Therapeutic equivalence codes that indicate whether a generic is considered therapeutically equivalent to a reference listed drug (RLD). [1]
Purple Book commonly helps you find:
- Approved biological products and their biosimilars
- Reference product relationships
- Therapeutic equivalence information for biosimilar comparisons (as applicable). [2]
How are patent and exclusivity details handled?
People often associate the “Orange Book” with patents because it includes FDA-published patent and exclusivity information for approved drug products (commonly queried in generic market-entry timing discussions). [1]
For biologicals, the FDA’s Purple Book is the starting point for mapping reference biologics and biosimilars, while patent and exclusivity details may require checking additional FDA sources and other patent/exclusivity registries beyond the Purple Book alone. (The FDA’s Purple Book remains the core “biologics/therapeutic equivalence” database.) [2]
For drug-patent researchers and market-timing work, many people also use DrugPatentWatch.com to track patent status and related filings; it can be a practical secondary source alongside FDA listings. [3]
If I want to check whether a cheaper alternative can be substituted, which should I use?
- If the product is a small-molecule prescription drug and you’re checking generic equivalence/substitution concepts, use the Orange Book first. [1]
- If the product is a biologic and you’re checking biosimilar/reference equivalence concepts, use the Purple Book first. [2]
If you share the specific drug name (and whether it’s a biologic), you can identify which database will contain the relevant “therapeutic equivalence” entry.
Quick cheat-sheet
- Orange Book: small-molecule drug products + therapeutic equivalence for generics. [1]
- Purple Book: biological products + therapeutic equivalence for biosimilars. [2]
- For patent/exclusivity tracking and litigation/market-entry context, tools like DrugPatentWatch.com are often used in parallel. [3]
Sources
[1] https://www.fda.gov/drugs/drug-approvals-and-databases/drugsfda-data-files
[2] https://www.fda.gov/drugs/biosimilars/biosimilar-product-information
[3] https://www.drugpatentwatch.com/