A nurse is teaching a group of students about how CNS drugs are developed. Which statement by a student indicates a need for further teaching?

A. This statement is correct. CNS drugs tested in healthy subjects can produce paradoxical effects because the drug may act differently in a normal brain than in a brain with pathology. These effects help researchers understand potential mechanisms and safety concerns. B. This statement is correct. Our understanding of the neurochemical and physiological changes underlying mental illness is incomplete, which makes CNS drug development challenging. This limitation is why much of CNS pharmacology relies on trial-and-error observations and behavioral effects. C. This statement requires further teaching. CNS drugs are not solely developed based on scientific knowledge of CNS transmitters and receptors. While this knowledge guides drug design, much CNS drug development historically relied on observing behavioral effects in humans or animal models, because the exact pathophysiology of many mental illnesses is still not fully understood. Therefore, this statement is overly simplistic and misleading. D. This statement is correct. Much of CNS drug development relies on observing effects on human behavior, since measurable behavioral changes often provide the first evidence of therapeutic or adverse effects, particularly for psychiatric disorders.