Understanding the Criteria: What Classifies a Drug a Drug?

October 12, 2025 •

5 min read

According to the U.S. Food and Drug Administration (FDA), a substance's intended use is a primary determinant in establishing what classifies a drug a drug. This legal and scientific definition extends beyond just prescription pills to include any article intended to diagnose, cure, mitigate, or prevent disease, or to affect the structure or function of the body.

Quick Summary

A drug is defined by its intended use, biological effect, and regulatory status, differentiating it from food and other products. Classification involves federal criteria from bodies like the FDA and DEA, considering pharmacological properties and potential for abuse to ensure safety and control.

Key Points

Intended Use is Paramount: A product’s marketing claims determine if the FDA regulates it as a drug, based on whether it’s meant to diagnose, treat, or prevent disease.
Legal Scheduling by DEA: The DEA classifies drugs into five schedules (I-V) under the Controlled Substances Act, based on their potential for abuse, accepted medical use, and risk of dependence.
Pharmacological Properties Matter: A substance is characterized by its biological effects on the body, including its mechanism of action (pharmacodynamics) and how the body processes it (pharmacokinetics).
Drugs vs. Supplements: Unlike drugs, dietary supplements are regulated as food, do not require premarket FDA approval for safety and efficacy, and cannot make disease-treatment claims.
Dynamic Classification: A drug’s classification is not static and can change based on new scientific evidence or shifts in abuse trends, as seen with evolving cannabis regulations.
Multi-layered System: A substance's classification often involves multiple criteria, including legal schedules, chemical properties, and therapeutic use, to ensure public health and safety.

The question of what classifies a drug a drug is not a simple one, as the answer involves a complex interplay of legal definitions, pharmacological properties, and regulatory oversight. Unlike food or cosmetic products, drugs are subject to rigorous evaluation by government agencies like the U.S. Food and Drug Administration (FDA) and the Drug Enforcement Administration (DEA) before they can be legally marketed and sold. This comprehensive system ensures public safety and regulates substances based on their potential for harm and therapeutic value.

The Role of 'Intended Use' and the FDA

At the core of a drug's classification is its "intended use," a concept established by the FDA. The intended use is determined by the manufacturer's claims on product labeling, in advertising, or through other promotional materials. For a substance to be legally defined as a drug, it must meet one of the following criteria under the Federal Food, Drug, and Cosmetic (FD&C) Act:

Therapeutic Intent: It is intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease. This applies to prescription medications like antibiotics and over-the-counter drugs like aspirin.
Structural or Functional Effect: It is intended to affect the structure or any function of the body. This captures a wide range of products, from hormonal birth control to some types of topical creams that alter physiological processes.
Pharmacopoeia Recognition: It is recognized in an official pharmacopoeia, such as the United States Pharmacopoeia.

This legal framework, based on intended use, means that the exact same chemical substance could be regulated differently depending on how it is marketed. For example, a product sold purely as a skin moisturizer is a cosmetic, but if the same formula is marketed to treat dermatitis, it becomes a drug and must meet FDA approval standards.

The DEA's Role: Controlled Substances and Scheduling

Beyond the FDA's therapeutic classification, the DEA classifies drugs based on their potential for abuse and dependence, as outlined in the Controlled Substances Act (CSA). This scheduling system, ranging from Schedule I to Schedule V, dictates the level of control and regulation for each substance.

The criteria for scheduling include:

Potential for Abuse: The likelihood of the substance being misused.
Accepted Medical Use: Whether it has a currently accepted medical use in the United States.
Dependence Liability: The potential for physical or psychological dependence.

Drug Schedules in the United States

Schedule I: High potential for abuse, no currently accepted medical use. Examples include heroin and LSD.
Schedule II: High potential for abuse, but with accepted medical use, and can lead to severe dependence. Examples include cocaine and fentanyl.
Schedule III: Moderate to low potential for dependence, with accepted medical use. Examples include anabolic steroids and Tylenol with codeine.
Schedule IV: Low potential for abuse and dependence, with accepted medical use. Examples include Xanax and Valium.
Schedule V: Lowest potential for abuse and dependence, with accepted medical use. Examples include certain cough preparations with small amounts of codeine.

Drugs vs. Dietary Supplements: A Critical Distinction

A common point of confusion is the difference between a drug and a dietary supplement. The key distinction lies in regulation and marketing claims, as dietary supplements are regulated as a category of food, not drugs.


Feature	Drug	Dietary Supplement
Regulation	FDA approval required for safety and efficacy before marketing.	FDA does not approve for safety and efficacy. Manufacturers are responsible for ensuring safety.
Intended Claims	Can make claims to diagnose, cure, mitigate, treat, or prevent disease.	Cannot make claims to treat diseases. Can only make structure/function claims related to general well-being (e.g., “calcium builds strong bones”).
Premarket Approval	Must undergo extensive clinical trials and premarket review by the FDA.	No premarket approval process required by the FDA.
Oversight	The FDA actively monitors manufacturing, labeling, and advertising.	The FDA can take action against unsafe products after they are on the market.

Pharmacological Properties: Mechanism of Action

Beyond regulatory definitions, a drug's classification can also be based on its pharmacological properties—how it affects the body at a biological level. This includes its mechanism of action, or the specific molecular target it interacts with to produce an effect. For instance, drugs are classified into therapeutic categories like analgesics (pain relievers), antidepressants, and beta-blockers, reflecting their intended clinical use.

Another layer of classification relates to how the drug behaves within the body, a field known as pharmacokinetics. This includes four stages: absorption, distribution, metabolism, and excretion (often abbreviated as ADME). Understanding these properties is crucial for determining dosage, predicting side effects, and managing drug therapies effectively.

The Interplay of Factors in Drug Classification

In practice, a drug's classification is rarely based on a single factor but rather a combination of its intended use, pharmacological properties, and legal status. The same substance could fall into multiple categories depending on the context. For example, morphine is a Schedule II controlled substance (legal classification) but is also an opioid (chemical classification) and a narcotic analgesic (therapeutic classification).

Regulatory bodies like the FDA and DEA collaborate to ensure that controlled substances with medical uses, such as opioid pain medications, are appropriately regulated to prevent misuse while remaining available for legitimate medical purposes. The classification process is dynamic and can change based on new scientific evidence, abuse trends, or emerging therapeutic applications. For example, the legal status of cannabis in the U.S. has undergone significant shifts, illustrating the evolving nature of drug classification.

Conclusion: A Multi-faceted Definition

Ultimately, the question of what classifies a drug a drug reveals a comprehensive and multi-faceted framework. It is a system designed to balance a substance’s potential therapeutic benefits against its risks, with legal and scientific criteria working in tandem. From the manufacturer’s stated intent and the substance's biological effects to its potential for abuse and its place in legal schedules, a drug's classification determines its regulation, accessibility, and safe use. Understanding these intricate classifications is essential for healthcare professionals, regulators, and consumers alike to navigate the world of medications and pharmacology effectively.

For more detailed guidance on the classification of products, refer to the FDA's official resources.

Frequently Asked Questions

The main difference is how they are regulated and marketed. A drug must undergo extensive clinical trials and FDA approval to prove its safety and effectiveness before being sold, and it can make claims to treat diseases. A dietary supplement is regulated as a food, does not require premarket FDA approval, and can only make structure/function claims, not disease-treatment claims.

The FDA determines a product's intended use by examining various factors, including the manufacturer’s claims on product labeling and in advertising, statements made by company representatives, and consumer perception of the product's purpose.

A controlled substance is a drug or chemical whose manufacture, possession, and use are regulated by the government under the Controlled Substances Act (CSA). The DEA classifies these substances into five schedules based on their medical use and potential for abuse and dependence.

A Schedule I drug has a high potential for abuse and no currently accepted medical use in the U.S. (e.g., heroin). In contrast, a Schedule V drug has a low potential for abuse and low risk of dependence, with accepted medical use (e.g., certain cough medicines).

Yes. An OTC medication is still considered a drug because it is intended to affect the structure or function of the body and is used to treat, prevent, or mitigate disease. The key difference is that it does not require a doctor's prescription.

Pharmacological properties describe a substance's biological effects and activities. These properties include its mechanism of action—how it interacts with the body—and pharmacokinetics—how the body absorbs, distributes, metabolizes, and excretes it.

No. The legal classification of a drug, such as its schedule under the CSA, can sometimes conflict with its known or potential medical uses. A prime example is cannabis, which is federally classified as Schedule I despite being legal for medical and recreational use in many states.