Abstract
This article challenges the recurrent claim that the concept of drug is scientifically indefinable or reducible to a legal, social, or normative construct. It argues that semantic and classificatory variability does not entail ontological indeterminacy: substances possess materially real and causally efficacious properties that constrain scientific classification, while the concepts constructed from those properties remain discipline-specific, situated, and epistemically mediated. Combining legal textual analysis, epistemology, logic, and terminology, the article distinguishes pharmacological, neuroscientific, legal, and lexicographic registers and examines how their conflation has contributed to the apparent indeterminacy of the concept. A structured process of individuation - moving from ontology to taxonomy, typology, and terminology - is used to reconstruct the concept and clarify the relation between causal properties and classificatory practices. The analysis shows that the term drug admits of more than one scientifically coherent intension, depending on disciplinary framework and explanatory purpose. In pharmacology, it denotes the broad class of exogenous chemical substances, other than nutrients or essential dietary ingredients, that produce biological effects. In neuroscience, it denotes the narrower subclass of psychotropic substances acting on the central nervous system and modifying mental processes. Neither definition is universally privileged outside its disciplinary domain. Narcotic drug, by contrast, is a stipulative legal category whose extension is determined through institutional designation and scheduling rather than through derivation from the scientific intension of drug. The article concludes that the claims of scientific indefinability examined here arise in substantial part from conflating semantic variability, scientific concepts, legal classifications, and moral or social representations.