### Question
How is the term primary mode of action defined?


### Answer
The term **primary mode of action** is defined in *21 U.S.C. § 353* as the following:

> the single mode of action of a combination product expected to make the greatest contribution to the overall intended therapeutic effects of the combination product

#### Citation:
  - *21 U.S.C. § 353*
  - Heading: **CHAPTER 9-FEDERAL FOOD, DRUG, AND COSMETIC ACT > SUBCHAPTER V-DRUGS AND DEVICES > Part A-Drugs and Devices**

