Definition
A drug is any substance — vegetable, animal, mineral, or synthetic — used or intended for use in diagnosing, curing, treating, mitigating, or preventing disease, or for altering the structure or function of the body. Legal definitions of the term operate across at least three distinct contexts, each with its own scope:
1. Pharmaceutical/regulatory meaning: Any article intended for use as a medicine, including substances used in the composition or preparation of medicinal products. This is the foundational meaning inherited from early common law and codified in modern food and drug statutes. Under federal law, the definition extends to articles intended to affect the structure or any function of the body, which is broad enough to capture products not traditionally thought of as medicines (vitamins, cosmetics with drug claims, certain devices).
2. Controlled substances meaning: In criminal law and regulatory enforcement, "drug" often functions as shorthand for controlled substance — a substance whose manufacture, distribution, possession, or use is regulated or prohibited under schedules established by statute. This meaning carries enforcement consequences entirely absent from the pharmaceutical sense.
3. Commercial/trade meaning: Historically, "drug" encompassed materials used in dyeing and chemistry — commodities of the apothecary trade — not solely medicinal preparations. This sense survives in older statutes and cases but is largely obsolete in modern usage.
Common Language
Modern common usage (Wiktionary): A substance used to treat illness or relieve symptoms; or, colloquially, a psychoactive or addictive substance ingested for recreational use, especially an illegal one. Also used loosely for any habit-forming thing.
Historical common usage (Webster's 1913): Webster's 1913 does not offer a useful substantive definition for this sense; the entry traces a now-obsolete verb form meaning to drudge or toil laboriously, reflecting a different etymological strand.
The legal gap is significant in two directions. First, the colloquial equation of "drug" with illegal or recreational substance is narrower than almost every legal definition, which includes lawful pharmaceuticals, over-the-counter medicines, and even some compounds with no psychoactive effect. Second, regulatory definitions are deliberately expansive — a product can be a "drug" under the Federal Food, Drug, and Cosmetic Act based solely on the claims made about it, not its chemistry — a result that would surprise ordinary readers who think of the category as defined by what a substance does rather than what a seller says about it.
Common Confusion
Drug vs. controlled substance: In casual legal writing these terms are used interchangeably, but they are not coextensive. Aspirin is a drug; it is not a controlled substance. Conversely, a substance may be a controlled substance even if it has no recognized medical use and would not qualify as a drug in the pharmaceutical sense. The confusion matters most in statutory interpretation: a criminal statute penalizing possession of a "controlled substance" does not reach possession of an unscheduled pharmaceutical, and a regulatory provision governing "drugs" may reach substances with no abuse potential.
Drug vs. device: Food and drug law draws a formal line between drugs (which achieve their purpose through chemical action or metabolism) and devices (which achieve their purpose through physical means). Combination products straddle this line, and the classification determines which regulatory pathway applies. Courts and agencies have litigated this boundary extensively.
Recognized Forms
/SUBTYPES
Controlled substance: A drug or substance listed on a regulatory schedule (Schedule I–V under the Controlled Substances Act) based on accepted medical use, potential for abuse, and risk of dependence. The scheduling tier determines the severity of applicable criminal penalties and the conditions under which legitimate use is permitted.
Prescription drug: A drug that may be dispensed only upon a licensed practitioner's order, distinguished from over-the-counter drugs available without a prescription. The distinction carries both regulatory and criminal significance (unauthorized distribution of prescription drugs is a separate offense from simple possession of a controlled substance).
New drug: A regulatory category under food and drug law for any drug not generally recognized among qualified experts as safe and effective for its intended use — requiring premarket approval before distribution in commerce.
Adulterated or misbranded drug: Drugs that fail to meet manufacturing standards or that bear false or misleading labeling; subject to regulatory seizure and criminal sanctions independent of whether the underlying substance is a controlled drug.
Why It Matters in Research
The term "drug" is one of the most definition-dependent words in legal research. Its meaning shifts not only across practice areas but within the same statute depending on which provision is at issue. Researchers working in criminal law will encounter "drug" as a proxy for the controlled substances schedules; researchers in administrative and regulatory law will encounter a dramatically broader definition shaped by legislative intent and agency interpretation; researchers in tort and products liability will encounter yet another functional definition centered on the pharmaceutical relationship between manufacturer, prescriber, and patient.
Historical sources compound the difficulty. Cases and statutes from the nineteenth and early twentieth centuries used "drug" to include dyeing materials, chemical reagents, and apothecary commodities that have no relationship to modern pharmaceutical or controlled substance law. Courts interpreting early adulteration statutes sometimes defined "drug" by reference to what apothecaries sold, not by pharmacological function. Researchers should not assume continuity of meaning across eras.
Jurisdictional variation in controlled substance schedules is a persistent trap. A substance may be scheduled under federal law but not under a given state's analog act, or vice versa. State definitions of "drug paraphernalia," "drug-free zones," and "drug trafficking" vary significantly, and the predicate definition of "drug" anchoring those provisions is not uniform.
The regulatory definition under food and drug law — shaped heavily by agency rulemaking and federal court interpretation — is substantially more expansive than anything the nineteenth-century sources contemplated. Researchers crossing between the criminal and regulatory corpora must treat these as parallel but non-identical definitional universes.
Historical Dictionary Support
Black's Law Dictionary (2nd Ed.) provides a workable foundational definition: "the general name of substances used in medicine; any substance, vegetable, animal, or mineral, used in the composition or preparation of medicines," with the additional note that the term extends to materials used in dyeing and chemistry. This captures the trade-and-apothecary sense that dominated early legal usage. The cases cited in that edition (Collins v. Banking Co.; U.S. v. Merck; Insurance Co. v. Flemming) reflect late nineteenth-century judicial efforts to give the term workable content in commercial and regulatory disputes — the pharmaceutical-regulatory superstructure of the twentieth century was not yet built.
The first edition of Black's offers no substantive entry for the term as it appears in this corpus, and the fragment reproduced here is from an unrelated maxim entry, confirming that "drug" had not yet attracted independent dictionary treatment by that edition's date.
What the historical dictionaries miss almost entirely is the modern bifurcation of the term into its regulatory (pharmaceutical) and criminal (controlled substance) branches — a division that became legally significant only with the development of federal drug scheduling law in the twentieth century. Neither edition of Black's anticipates the claim-based definition central to modern food and drug regulation, nor the scheduling framework that drives contemporary criminal enforcement.
Jurisdictional Note
Federal law supplies the two dominant definitional frameworks: the Federal Food, Drug, and Cosmetic Act governs the pharmaceutical and regulatory meaning; the Controlled Substances Act governs the criminal scheduling framework. State laws adopt their own controlled substance schedules, which may differ from federal schedules, and state analog acts extend liability to unscheduled substances with similar chemistry or effects. Researchers should verify which definitional regime controls for the jurisdiction and statute at issue before relying on any single source.
Encyclopedia Cross-Reference
Drug Conspiracy (The Law Mind Criminal Law Encyclopedia)
Food and Drug Administration — Drug and Device Approval and Regulation (The Law Mind Administrative Law & Government Encyclopedia)
Drug Manufacturing and Cultivation (The Law Mind Criminal Law Encyclopedia)