### Question
How is the "isomer" defined?


### Answer
The term **isomer** is defined in *21 U.S.C. § 802* as follows -

> the optical isomer, except as used in schedule I(c) and schedule II(a)(4)

#### Citation:
  - *21 U.S.C. § 802*
  - Heading: **CHAPTER 12-MEAT INSPECTION > SUBCHAPTER I-CONTROL AND ENFORCEMENT > Part A-Introductory Provisions**

