How are "controlled substances" defined?

The definition of "controlled substances" specifically refers to drugs that are regulated due to their potential for abuse, dependence, or misuse. This regulation is put in place to protect public health and safety, ensuring that substances which may lead to addiction or be used illegally are monitored and managed. Controlled substances are categorized into schedules based on their potential for abuse, medical uses, and safety.

The other choices do not accurately reflect this definition. Over-the-counter medications typically do not fall under the category of controlled substances, as they are generally deemed to have a low potential for abuse. Natural remedies and herbal supplements usually lack the regulatory oversight that applies to controlled substances because they are not classified with the same level of potential risk for misuse. Thus, the correct answer highlights the specific regulatory framework surrounding substances that could lead to higher risks of addiction and public health issues.