National Drug Code (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 with certain structure rules that apply depending on the length of certain segments while keeping in mind that based on new FDA validation procedures an NDC code assigned to one product is unique and cannot 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. 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. 
