Allergic reactions to inactive ingredients in medications

An allergic reaction occurs when your body's immune system overreacts to a substance such as food, pollen, pet dander, or a medication. Often, people are allergic to a medication's main ingredient. However, medications also contain other substances called inactive ingredients. Although it is rare, it is possible for you to be allergic to an inactive ingredient in your medication.

What is an inactive ingredient?

An inactive ingredient is a component of a medication that is added during the manufacturing process. Examples of inactive ingredients include fillers to increase the bulk of the powder used to make tablets or capsules as well as film coatings and binders used to hold tablets together and to control how fast or slow a medication releases into your body.

Other inactive ingredients include dyes to add color, flavoring agents to improve the taste, and preservatives to prevent microbial growth. Some medications also contain gelatin, egg, lactose, milk protein, gluten, latex, or soy oil, which are also considered inactive ingredients.

Can you be allergic to an inactive ingredient?

Although you can be allergic to an inactive ingredient in your medication, it is very rare. Allergy symptoms most often occur within one hour of taking the medication, but some reactions may occur hours, days, or weeks later.

Allergy symptoms include skin rash, hives, itching, fever, swelling, and anaphylaxis, which is a very rare life-threatening reaction where your blood pressure suddenly drops and your airways narrow.

If you experience any allergy symptoms, call your doctor or pharmacist right away. If you have a severe reaction, call 911 for emergency care.

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Where can you find a list of inactive ingredients in your medication?

Inactive ingredient information for over-the-counter medications is listed on the packaging. Inactive ingredients for prescription medications may be found on the written information you receive with your medication, or you can ask your pharmacist.

It is important to check the most current inactive ingredient list for your medication, because ingredients may change over time. The inactive ingredients may be different between brand and generic versions of the same medication.

For more information about inactive ingredients in medications, visit the following:

• Food and Drug Administration Inactive Ingredient Database
• Color additives

See also:

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AHFS® Patient Medication Information is used with permission. ©2025, the American Society of Health-System Pharmacists, Inc. (ASHP). The ASHP Data is a part of the AHFS Drug Information®️; ASHP is not responsible for the accuracy of transpositions from the original context.