The National Drug Code is the FDA's universal product identifier for a human drug: a three-segment number that names the labeler, the specific formulation and the package size.
Every drug marketed in the United States must be listed with the FDA and assigned an NDC. The number is not a licence or an approval — it is an inventory identifier. A product can hold an NDC and still be unapproved, withdrawn or under recall.
The FDA publishes NDCs in a 10-digit form with three possible segment shapes (4-4-2, 5-3-2 and 5-4-1). Electronic claims require an 11-digit form in a fixed 5-4-2 shape, which is why the same drug appears with two different-looking codes depending on whether you are reading an FDA listing or a claim.