Every FDA-regulated pill sold in the U.S. is required to carry a unique imprint — a combination of letters, numbers, or symbols stamped or embossed on its surface — that encodes the manufacturer and drug identity. By recording the imprint together with the pill's shape and color, you can cross-reference a database like PillID to confirm exactly what medication you have.
How to Read a Pill Imprint Code — Complete Guide
Every prescription and over-the-counter tablet or capsule sold in the United States carries a unique stamped or printed code called an imprint. These codes are not random — they are a regulated identification system that allows anyone, from a pharmacist to a poison control specialist to a concerned parent, to determine exactly what a pill is. This guide walks you through how that system works and how to use it.
Why Imprints Exist: The Legal Requirement
Pill imprints did not always exist. It was not until 1995 that the U.S. Food and Drug Administration made them mandatory under regulations stemming from the Poison Prevention Packaging Act and subsequent FDA rulemaking (21 CFR Part 206). Before that, many tablets were plain, making identification in emergency situations extremely difficult.
Under current FDA rules, every solid oral dosage form — every tablet and every capsule — marketed in the United States must bear a unique imprint that identifies both the drug product and the manufacturer or distributor. The imprint must be legible and permanent, meaning it cannot wash off or fade under normal handling. This allows healthcare providers and poison control centers to positively identify any pill found in a home, a hospital, or an emergency setting.
Key fact: The FDA maintains the National Drug Code (NDC) directory, and imprint codes can be cross-referenced against it to return the exact drug name, strength, manufacturer, and dosage form — the same data PillID uses to power its identifier.
Anatomy of a Pill Imprint
An imprint can contain letters, numbers, or a combination of both. It may appear on one side of the tablet or on both sides. Understanding the components helps you read the code accurately.
Letters
Letters in an imprint almost always represent the manufacturer or distributor. For example, the letter "M" inside a square box typically indicates Mallinckrodt Pharmaceuticals. "GG" is a legacy code associated with Sandoz/Geneva. "IP" denotes Amneal Pharmaceuticals. "L" alone usually signals LNK International, a major manufacturer of store-brand OTC medications. Knowing common manufacturer prefixes helps narrow down a search before you even look up the number.
Numbers
The numeric portion of the imprint typically identifies the specific drug product and strength within that manufacturer's line. Together, the letters and numbers form a unique combination. Two manufacturers may use the same number, but the letter prefix makes the full code unique.
Scored Lines
Many tablets have a scored line — a groove pressed into the surface — that allows the tablet to be split. This is a physical feature, not part of the imprint code itself, but it is useful to note when describing a pill. A tablet described as "white, round, scored" with a particular imprint is much easier to identify than one described only by its code.
Reading a Two-Sided Imprint
Many pills carry different markings on each side. When entering an imprint into an identifier tool, you typically enter the front and back codes separately. To do this correctly:
- Lay the pill flat on a clean white surface under good light.
- Note every character on the first side — letters, numbers, and any separating slash or dash.
- Flip the pill and note the second side the same way.
- Record the imprint as "Side 1 / Side 2" — for example, "M / 365" means the letter M is on one face and the number 365 is on the other.
Order matters less than completeness. If a pill has "G" on one side and "3719" on the other, entering both correctly is what produces an accurate result. Most pill identifier databases accept either combination.
Common Imprint Formats and Real Examples
Here are four of the most commonly encountered imprints and what they mean:
- L484 — White, oblong tablet. Acetaminophen 500 mg (generic Tylenol). Manufactured by LNK International. Sold as store-brand pain relief at major retailers nationwide.
- M365 — White, oblong tablet. Hydrocodone bitartrate 5 mg / acetaminophen 325 mg. A Schedule II controlled opioid combination. The "M" in a square box indicates Mallinckrodt.
- IP 466 — White, oval tablet. Ibuprofen 600 mg. The "IP" prefix belongs to Amneal Pharmaceuticals. Requires a prescription at this strength in some contexts.
- GG 249 — White, rectangular (bar-shaped) tablet. Alprazolam 2 mg (generic Xanax). Manufactured by Sandoz. A Schedule IV controlled substance. Note: counterfeit pills mimicking this imprint are extremely prevalent — if there is any doubt about the source, do not assume the imprint is genuine.
WARNING: Counterfeit pills that replicate legitimate imprints are a serious and growing public health crisis. A pill bearing the GG 249 or M30 imprint purchased outside a licensed pharmacy may contain illicitly manufactured fentanyl. An imprint alone does not guarantee a pill is authentic if the source is unknown. When in doubt, do not take it.
Tips for Reading Worn or Damaged Imprints
Tablets stored loose in a pocket, bag, or non-original container can accumulate wear that makes the imprint difficult to read. These techniques can help:
- Angled light: Hold the pill under a direct light source — a phone flashlight works well — and tilt it at a 45-degree angle. The shadows cast into the stamped recesses make letters and numbers much more visible.
- Magnification: A phone camera zoomed to 2–3x and photographed on a white background will often reveal detail invisible to the naked eye.
- Partial entry: If only part of the imprint is legible, enter what you can. Many pill identifier tools support wildcard or partial searches. Even one or two characters, combined with shape and color, can narrow results significantly.
- Note physical characteristics: Color, shape (round, oval, oblong, capsule-shaped, pentagon, diamond, octagon), size in millimeters, and the presence or absence of a score line are all searchable fields that can compensate for an unreadable imprint.
When You Cannot Read the Imprint At All
Sometimes the imprint is completely absent — the pill has been in water, coated tablets have had their coating rubbed off, or the tablet simply cannot be positively identified. In that situation, the safest course is to contact your pharmacist. Pharmacists have professional access to drug identification resources and can often identify a pill from physical characteristics alone. If the situation involves a possible ingestion or overdose, call Poison Control immediately at 1-800-222-1222 — they are available 24 hours a day, 7 days a week, and the call is free and confidential.
Do not attempt to identify a completely unreadable pill by taste, smell, or texture. Never take or give a pill that cannot be positively identified.
Frequently Asked Questions
What is a pill imprint and why does every pill have one?
A pill imprint is a combination of letters, numbers, or symbols stamped or embossed on a tablet or capsule. The FDA requires all solid oral prescription and over-the-counter medications sold in the United States to bear a unique imprint. This allows healthcare professionals, pharmacists, patients, and poison control specialists to positively identify any tablet — its active ingredient, strength, and manufacturer — without a label or packaging.
How do I read a pill imprint to identify a medication?
Look at both sides of the tablet. Record all letters and numbers, noting the order and any dividing lines (score lines). Some imprints include only numbers, some only letters, and many combine both. The imprint is then cross-referenced against a pill identification database — like the one maintained by the U.S. National Library of Medicine — or entered into an online pill identifier tool. Matching the imprint with the tablet's color, shape, and size improves accuracy.
What if a pill has no imprint?
A pill without any imprint is almost certainly not an FDA-regulated prescription drug, since imprints are legally required. Unmarked tablets may be vitamins, herbal supplements, homeopathic products, or — more dangerously — illicit drugs pressed to look like pharmaceuticals. If you find an unmarked pill and are unsure what it is, do not take it. Contact your pharmacist or call Poison Control (1-800-222-1222) for guidance.
Why might two different pills have similar-looking imprints?
Different manufacturers may produce tablets with imprints that look similar to each other — for example, numbers only. Always confirm pill identity using multiple characteristics together: imprint, color, shape, and size. A pill identifier database cross-references all of these factors to narrow results. When in doubt, a pharmacist can confirm pill identity quickly and at no cost by looking it up in a pharmaceutical reference database.
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