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Lactaid Fast Act Side Effects

Generic name: lactase

Medically reviewed by Last updated on Feb 4, 2021.

Note: This document contains side effect information about lactase. Some of the dosage forms listed on this page may not apply to the brand name Lactaid Fast Act.

For the Consumer

Applies to lactase: oral tablet, oral tablet chewable

What are some side effects that I need to call my doctor about right away?

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

  • Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.

What are some other side effects of this drug?

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if you have any side effects that bother you or do not go away.

These are not all of the side effects that may occur. If you have questions about side effects, call your doctor. Call your doctor for medical advice about side effects.

You may report side effects to the FDA at 1-800-332-1088. You may also report side effects at

For Healthcare Professionals

Applies to lactase: oral capsule, oral liquid, oral tablet, oral tablet chewable


In general, side effects have not been reported with the use of lactase (the active ingredient contained in Lactaid Fast Act) [Ref]

More about Lactaid Fast Act (lactase)

Consumer resources

Other brands
Lactaid, Dairy Ease, Lac-Dose, Lactaid Ultra, ... +2 more

Related treatment guides


1. "Product Information. Lactaid (lactase)." McNeil Consumer Healthcare, Fort Washington, PA.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.