How do I decode the three segments of an NDC number?

Segment 1 — the labeler code

Four or five digits, assigned by the FDA. It identifies whoever is legally responsible for the label, which need not be the manufacturer: repackagers, relabelers and private-label distributors all hold their own labeler codes.

Codes are issued in sequence and never reused, so a low labeler code usually signals an old company and an old code still resolves to a name even after the firm is gone.

Segment 2 — the product code

Three or four digits, assigned by the labeler rather than the FDA, and unique only within that labeler's range. It identifies one specific formulation: a strength in a dosage form.

Change the strength, the dosage form or the formulation and you need a new product code. Change only the box size and you do not.

Segment 3 — the package code

One or two digits identifying the commercial package: a bottle of 30, a bottle of 90, a carton of five vials. This is the segment that appears on the outer carton barcode and the one payers price against.

The three 10-digit shapes

Nothing on the package says which shape it is. You infer it from the segment lengths, which is why the hyphens matter: strip them and the original segmentation cannot be recovered.