The CSA defines and regulates:

The Controlled Substances Act (CSA) specifically defines and regulates controlled substances, which are drugs that have a potential for abuse and dependency. This legislation classifies substances into different schedules based on their medical use, potential for abuse, and safety or dependence liability. The act aims to prevent drug abuse and protect public health by ensuring that controlled substances are prescribed and dispensed only for legitimate medical purposes.

The CSA outlines strict requirements for the handling of these substances, including registration of practitioners, record-keeping, and reporting. This careful regulation is important to control the supply of potentially dangerous drugs and to prevent misuse.

In contrast, over-the-counter drugs, prescription-only medications, and herbal supplements do not fall under the same stringent regulations as controlled substances. Over-the-counter medications are generally considered safe for public use without a prescription, while prescription-only medications can include a broader range of drugs, not all of which are classified as controlled substances. Herbal supplements are typically not regulated by the CSA at all and are instead governed by dietary supplement laws, which have different requirements and safety standards. Thus, the correct answer highlighting the focus of the CSA is indeed on controlled substance medications.