What is a controlled substance?

A controlled substance is defined as a drug that is regulated by law according to its potential for abuse, therapeutic value, and safety. In this context, the term "schedule" refers to a classification system that categorizes substances based on their accepted medical use and the degree of regulation required to control their distribution and use. This scheduling plays an essential role in ensuring that substances with a high potential for abuse, like certain narcotics and stimulants, are tightly regulated to prevent misuse and protect public health.

The other options depict substances in a manner that does not align with legal definitions. For instance, substances consumed freely do not have any legal restrictions, and medications available without a prescription are not necessarily controlled since they can be safely used without medical supervision. Likewise, substances used solely for recreational purposes may not fall under the regulatory framework that governs controlled substances, as many such substances might lack legal classification or might be considered illegal entirely.