What is the primary characteristic of a Schedule I drug?

A Schedule I drug is characterized primarily by its high potential for abuse. This classification, as defined by the Controlled Substances Act, includes substances that have no accepted medical use in the United States and are deemed to have a high risk of leading to severe psychological or physical dependence. Drugs in this category, such as heroin and LSD, are viewed as particularly dangerous due to their potential for addiction and the lack of approved medical applications. Hence, the emphasis on the high abuse potential distinctly sets Schedule I substances apart from those in other schedules which may have recognized medical uses and varying levels of abuse potential.