Final answer:
Schedule I controlled substances are drugs with no accepted medical use in the US and a high potential for abuse.
Step-by-step explanation:
The substances in Schedule I are best described as drugs with no accepted medical use in the US, which also have a high potential for abuse, and for which there is no provision for safe use in treatment under medical supervision. Therefore, the correct answer to the student's question is option 1: drugs with no accepted medical use in the US. It's important to note that psychoactive drugs can vary widely in terms of their potential for abuse and their accepted medical uses.