On almost every medicine package in the United States, usually near the barcode, there is a string of digits split by hyphens into three groups. It is on the carton, on the manufacturer’s bottle, and often on the pharmacy label as well. People ask what is an NDC number for a practical reason: they are holding a package and want to know whether that code can tell them what is inside, and whether it is worth writing down.
An NDC number, or National Drug Code, is the three-segment identifier that marks each drug product listed with the U.S. Food and Drug Administration for sale in the United States. The first segment identifies the labeler, the second the specific product (name, strength and form), and the third the package size and type. It identifies the package, not the tablet inside.
That last distinction is the useful part, and it is the reason the code is worth understanding rather than ignoring.
What is an NDC number, segment by segment
Federal drug listing rules, in 21 CFR Part 207, set out the format. An NDC is a numeric code in three segments, and each segment answers a different question.
- The labeler code is the first group. It is assigned by FDA to the company whose name appears on the label. That company might be the manufacturer, but it might also be a repackager, a relabeler, or a distributor selling the product under its own brand. Two boxes of the same medicine from two different companies will start with two different labeler codes.
- The product code is the middle group. Within one labeler, it identifies a specific product: a particular medicine at a particular strength in a particular dosage form. The rules require a new product code whenever something that matters changes, including the strength, the form, the name, or the tablet’s distinguishing features such as its size, shape, color or imprint.
- The package code is the last group. It identifies the package size and type. A bottle of 30 and a bottle of 90 of the same tablets share a labeler code and a product code and differ only here.
Read left to right, then, an NDC says who put this on the market, which of their products it is, and what container it came in. Nothing in it describes the tablet directly. That job belongs to a different code, covered below.
Why an NDC is sometimes 10 digits and sometimes 11
This is the point that confuses almost everyone, including people who work with the codes daily.
The listing rules allow the segments to have different lengths. The labeler code can be 4, 5 or 6 digits, the product code 3 or 4 digits, and the package code 1 or 2 digits, in a handful of permitted combinations. The common configurations on packaging are 4-4-2, 5-3-2 and 5-4-1, all of which add up to 10 digits. The hyphens on the package show you which configuration a given labeler uses.
Billing and insurance systems do not like variable-length codes, so they use a fixed layout where every segment has a set width: five digits, then four, then two, for 11 in total. To fit a 10-digit package code into that layout, a zero is added to the front of whichever segment is short. The 4-digit labeler gets a leading zero, or the 3-digit product code does, or the 1-digit package code does. The hyphens are usually dropped at the same time.
So the 10-digit code on your box and the 11-digit code on an insurance statement are the same code, written two ways. If you ever need to compare them, put the hyphens back in and look for the added zero.
One more detail worth knowing: the rules now also permit 6-digit labeler codes, which produce 11-digit codes on the package itself. Most of what is on pharmacy shelves today still uses the 10-digit configurations, but a genuinely 11-digit NDC on a carton is not a mistake. FDA has also finalized a move to a single uniform 12-digit format, but it does not take effect until 2033, so the 10 and 11 digit codes described here are what you will see for years yet.
Where to find the NDC on a box and on a pharmacy label
On a manufacturer’s carton or stock bottle, the NDC is printed as part of the label, typically preceded by “NDC” and usually close to the barcode. It is one of the few things on the package that is the same on every unit of that product.
Pharmacy dispensing labels vary by pharmacy. Many print the NDC of the stock bottle the tablets came from, often near the manufacturer’s name and the fill details, because it records exactly which product was dispensed. Some do not print it at all. If it is there, it is the most precise description of what you were given, more precise than the medicine name alone, because it points to one labeler’s one product in one package. It is also not the same as the Rx number printed on the same label, which what does Rx mean explains.
NDC, imprint and lot number: three codes, three jobs
A package carries more than one code, and they are easy to confuse.
- The NDC identifies the product and package, as above. It is the same on every carton of that product ever sold.
- The imprint is the marking pressed or printed on the tablet or capsule itself. Federal rules require it on most solid oral medicines for human use so that a loose tablet can be tied back to a specific product and manufacturer. This is the code that identifies a pill with no packaging around it. How those markings work is covered in what pill imprint codes mean.
- The lot number (sometimes “batch”) identifies one production run. It changes from batch to batch of the same product and matters for recalls and quality questions, not for identification.
A simple way to hold the three apart: the NDC says what product this is, the imprint says what tablet this is, and the lot says which batch it came from. When a tablet is loose on the counter with no box, only the imprint is still attached to it, which is why photographing the marking is the first step in identifying it.
How to look up an NDC number
Two public sources cover most of what you will find on a pharmacy shelf.
FDA’s National Drug Code Directory is the official list. It contains the products that labelers have submitted to FDA in their electronic listing files, and FDA updates it daily. Searching by the code, or by a product name, returns the labeler, the product, the dosage form, the strength and the package description. FDA is careful to say that inclusion in the directory does not mean it has verified the listed information, and that an NDC on a label does not indicate FDA approval of the product. The code is an identifier, not an endorsement.
DailyMed, run by the National Library of Medicine, is often the more useful stop for a person at home. It hosts the current labeling for listed products, and you can search it by NDC. The entry for a product shows its labeling, including the packaging information, and for many tablets and capsules a description of the product’s appearance and imprint, sometimes with an image. That is the bridge between the two codes: the NDC on the box takes you to the labeling, and the labeling tells you what the tablets inside should look like.
The practical sequence, if you want to check a package against its contents:
- Read the NDC off the carton or the pharmacy label, hyphens included.
- Search it on DailyMed and open the labeling for that product.
- Find the section describing the product, which lists the imprint, shape and color the tablets are supposed to have.
- Compare that with the tablet in your hand.
If the two agree, the tablet belongs to the package. If they do not, the tablet was not from this package, or the package is not what it claims to be, and either way a pharmacist should see both.
What an NDC tells you when a refill looks different
This is where the code earns its place in a medicine cabinet. When a refill arrives looking nothing like last month’s, the usual explanation is that the pharmacy dispensed a different manufacturer’s version of the same medicine, which is ordinary and described in why your refill looks different. The NDC makes that explanation checkable rather than a guess.
A different manufacturer means a different labeler code, so the first segment of the NDC on the new label will differ from the old one. And because the rules require a new product code whenever a tablet’s size, shape, color or imprint changes, even the same manufacturer changing the look of a product produces a new code. Comparing the NDC on the old label with the NDC on the new one tells you, in a few seconds, whether you are looking at a different company’s product, a changed product from the same company, or exactly the same product as before.
For the fuller picture on what does and does not have to match between a brand medicine and its generic equivalents, see generic vs brand name drugs. The short version is that the active ingredient, strength and form must match, the appearance is free to differ, and the NDC records which specific version you were given.
A small habit worth keeping
You do not need to memorize any of this. Two things are enough.
First, when a new medicine arrives, photograph the pharmacy label and the box, so the NDC is on record without any effort. Second, when something looks wrong, put the NDC into DailyMed before you worry. Most of the time it confirms an ordinary manufacturer switch, and when it does not, you walk into the pharmacy with a specific question instead of a vague one. A pharmacist can confirm what was dispensed from their own records in a couple of minutes, and that is the right way to settle anything you plan to act on.