How to Read a Drug Label for Allergens: Finding the Inactive Ingredients

Where the inactive ingredients are depends on the kind of medicine. On an over-the-counter product, look for the “Inactive ingredients” heading on the Drug Facts panel. On a prescription, look past the label your pharmacy prints: the list is in the manufacturer’s prescribing information, generally in the Description section, which you can read for free on DailyMed. In both cases, the NDC number is what ties the label you are reading to the exact product you are holding.

Over-the-counter: the Drug Facts panel

Over-the-counter medicines carry a standardized Drug Facts panel, and federal rules fix the order of its sections. “Inactive ingredients” is the last required section, after “Other information.” Three things are useful to know when you get there:

• Each one is named. The section must list each inactive ingredient by its established name.
• The order is alphabetical. For over-the-counter drugs that are not also cosmetics, the inactive ingredients must be listed in alphabetical order. That is the opposite of a food label, which lists ingredients by weight, from most to least. On a Drug Facts panel, the first ingredient is not necessarily the main one, so position tells you nothing about amount. (Products that are both a drug and a cosmetic, such as fluoride toothpaste or antibacterial mouthwash, follow cosmetic listing rules instead.)
• There may be a phone number. Drug Facts may end with a “Questions?” line and a number to call. That is a direct route to asking the company where an ingredient came from.

A few ingredient warnings also appear on Drug Facts. The phenylalanine statement for products sweetened with aspartame, for example, belongs under “Other information.” Why so few ingredients get a warning at all is the subject of our guide to why medication labels do not have to list allergens.

Prescription: look past the pharmacy label

The label your pharmacy prints is built around your prescription: your name, the drug, the strength, and the directions. It usually does not list the inactive ingredients. Those are in the manufacturer’s prescribing information, the long folded sheet often called the package insert. The FDA says that for prescription drugs, ingredients will generally be listed in the Description section. In newer-format labeling, that section is numbered 11, and federal rules require it to include the drug’s ingredient information.

Two other parts of the prescribing information are worth a look. Required ingredient warnings, such as those for sulfites, sit in the warnings or precautions sections. And newer-format labeling describes what each dosage form looks like, including its color, shape, and imprint, which helps you confirm the label matches the pill.

DailyMed: the free place to read any label

DailyMed is run by the National Library of Medicine, part of the National Institutes of Health. It holds the labeling that companies submit to the FDA: prescribing information and patient labeling for prescription drugs, Drug Facts for over-the-counter drugs, and labeling for other products, including dietary supplements. It is free and needs no account.

Two cautions come straight from DailyMed and the FDA. First, DailyMed shows the most recent labeling a company has submitted, which may not be identical to the paper labeling packed with a particular product. Second, the FDA advises making sure the label you are reading matches your product, including the product name and the manufacturer or distributor. A search for the drug name alone can return labels from many companies, each with its own inactive ingredients.

The NDC: the number that pins the exact product

The National Drug Code is the FDA’s identifier for a drug product. It has three segments: one for the labeler (the company), one for the product, and one for the package size and type. It is usually printed on the manufacturer’s packaging, and for a prescription your pharmacist can tell you the NDC of what was dispensed. Searching DailyMed by NDC, rather than by drug name, is the surest way to land on the label for the product you actually have.

One nuance: the labeler is not always the company that made the pill. The FDA notes that a labeler can be a manufacturer, a repackager, or a relabeler. If your prescription came from a repackaged supply, ask your pharmacist for the NDC of what they dispensed.

What the ingredient list will not tell you

• Where an ingredient came from. A name like “starch” may not say which plant it is from. The FDA says very few oral drugs contain wheat starch and that starch used to make other ingredients is often corn or potato, but the list may not specify. An ingredient derived from a food allergen appears under its own name, with no “Contains: milk” style statement required.
• What is inside a flavor or color. For prescription drugs that are not taken by mouth, the rules allow flavorings to be listed simply as flavorings and colors as “coloring,” unless a specific color must be named. Our guide to dyes in medication covers FD&C Yellow No. 5, the dye federal rules single out for naming.
• Whether it still applies. Labels describe one product at one point in time. When your refill comes from a different company, the list can be different, which our guide to generic vs. brand-name drugs explains.

A quick way to check any medicine

• Over the counter: read “Inactive ingredients” on the Drug Facts panel, and use the “Questions?” number if a source is unclear.
• Prescription: get the NDC from the packaging or your pharmacist, then read the Description section on DailyMed.
• Unclear source: ask your pharmacist or call the manufacturer about the specific ingredient.
• Use the app: the AllergenMeds app flags ingredients like these in the exact product you look up, so you do not have to work through the list alone.

This guide is for education only, not medical advice. Always talk to your doctor or pharmacist before starting, stopping, or switching any medication.