The national drug code (NDC) is a unique product identifier used in the United States for drugs intended for human use. The Drug Listing Act of 1972 requires registered drug establishments to provide the Food and Drug Administration (FDA) with a current list of all drugs manufactured, prepared, propagated, compounded, or processed by it for commercial distribution. Drug products are identified and reported using the NDC.

There are several alternative drug classification systems in addition to NDC that are also commonly used when analyzing drug data, such as Generic Product Identifier (GPI).

The national drug code is a unique 10 or 11 digit, 3-segment numeric identifier assigned to each medication listed under Section 510 of the US Federal Food, Drug, and Cosmetic Act. The segments identify the labeler or vendor, product (within the scope of the labeler), and trade package (of this product).

While the labeler code is assigned by the FDA, both the product and package segments are assigned by the labeler. While in the past labelers may have had the opportunity to reassign old product codes no longer used to new products, according to the new FDA validation procedures, once an NDC code is assigned to one product (defined by key properties including active ingredients, strength, and dosage form) it may not be later reassigned to a different product.

NDC codes exist in one of the following groupings of digits into segments: 4-4-2, 5-3-2, 5-4-1, 6-3-2, or 6-4-1.

The following NDC structure rules apply depending on the length of certain segments. These rules include the 11 digit format. Unless stated otherwise, search for drug codes using the 10 digit format.

The official FDA format for NDCs separates the 3 segments with dashes. This is the format in which the NDC must be submitted by labelers since mandatory electronic listing was established in June 2009.

While the NDC is a 10-digit identifier, confusion exists because of a proliferation of different notations and variants.