Which of the following classes of drugs has no accepted medical use and is considered high risk for abuse?

The classification of drugs is based on their medical use and potential for abuse, as defined by the Controlled Substances Act. Among the various classes, Schedule I drugs, which fall under the classification of CI, have no accepted medical use in the United States and are recognized as having a high potential for abuse. This classification includes substances like heroin, LSD, and marijuana, at least federally, as they lack an accepted safety profile and are deemed unsafe even under supervised medical use.

In contrast, Schedule II drugs (CII), while also having a high potential for abuse, are recognized for having accepted medical uses. These include opioids and certain stimulants that can be prescribed but are strictly regulated due to their risk. Schedule III (CIII) and Schedule IV (CIV) drugs also have accepted medical uses but present a lower potential for abuse compared to CI and CII substances.

Therefore, class CI is the only category without recognized medical use and is classified as high risk for abuse, making it the correct answer to the question.