Section 201(h) of the FD&C Act: Device Definition and Criteria

Section 201(h) of the Federal Food, Drug, and Cosmetic Act, codified at 21 U.S.C. § 321(h), is the statutory provision that defines what counts as a “device” under federal law.¹ A product falls within the definition if it is an instrument, apparatus, implement, machine, contrivance, implant, in vitro reagent, or similar article (including any component, part, or accessory) that satisfies at least one of three criteria — and does not achieve its primary intended purpose through chemical action within or on the body or through being metabolized. Once a product meets that definition, it is subject to FDA oversight, and marketing it without the required authorization is a federal violation.

The Three Criteria That Trigger Device Status

A product only has to satisfy one of the following three prongs to be a device:

Compendium recognition. The product is recognized in the official National Formulary, the United States Pharmacopeia, or any supplement to either.
Diagnosis or treatment purpose. The product is intended for use in the diagnosis of disease or other conditions, or in the cure, mitigation, treatment, or prevention of disease in humans or other animals.
Effect on structure or function. The product is intended to affect the structure or any function of the body of humans or other animals, even without any disease-related claim. Surgical tools, orthopedic implants, and physical therapy equipment typically qualify here.

These prongs are read broadly. A product does not need a medical setting, a prescription requirement, or a hospital buyer to satisfy any of them. What matters is whether the manufacturer intends the product for one of these purposes and communicates that intent through its labeling, marketing, or design.

The Chemical Action Exclusion

Meeting one of the three prongs is not enough on its own. The statute excludes any product that achieves its primary intended purpose through chemical action within or on the body, or that depends on being metabolized to work.¹ The FDA reads this exclusion as applying across all three prongs, not just the diagnosis and structure/function prongs. A product that would otherwise qualify as a device is not a device if chemistry or metabolism is doing the primary work.²

The practical takeaway is that devices work through physical, mechanical, thermal, or electromagnetic means. A pacemaker delivers electrical impulses. A hip replacement provides structural support. A surgical laser cuts tissue with focused energy. If a product’s primary mechanism involves a chemical reaction in the body or requires the body to metabolize it, the product sits on the drug side of the line.

The dividing line is not always clean. Bone cement, for example, hardens mechanically inside the body but involves a chemical polymerization reaction to get there. In cases like that, the FDA looks at whether the chemical action is the primary mechanism or merely incidental to a physical function. A product with a chemical component can still qualify as a device when the chemistry is secondary.

Intended Use Decides Classification

Whether a product falls under Section 201(h) usually depends less on what the product physically is than on what its maker says it does. The FDA regulation at 21 CFR 801.4 defines “intended use” as the objective intent of the persons legally responsible for the product’s labeling.³ That intent can be shown through labeling claims, advertising, product design, and the circumstances surrounding distribution.

The FDA looks beyond the printed label. Oral statements by sales representatives, promotional materials at trade shows, and website copy all count as evidence of intended use. Market a general-purpose wearable sensor with claims that it “monitors heart rhythm abnormalities,” and those claims create a diagnostic intended use that pulls the sensor into device territory. Market the same sensor as a fitness tracker with no health condition claims, and it may stay outside the definition.

There is one important limit. The FDA will not treat a manufacturer as intending an unapproved use based solely on knowledge that healthcare providers are using the device off-label.³ Awareness that doctors prescribe a cleared device for a different purpose does not, by itself, create a new intended use. That changes the moment the manufacturer actively promotes the off-label use through marketing or sales materials.

Device or Drug?

Section 201(g) defines a “drug” using nearly the same three-prong structure as the device definition: compendium recognition, diagnosis or treatment intent, and intent to affect body structure or function.¹ A single product can technically satisfy both definitions at once. The chemical action exclusion is what separates them: chemistry or metabolism as the primary mechanism means drug; physical or mechanical means as the primary mechanism means device.

This matters because the two regulatory tracks are entirely different. Drugs go through the FDA’s drug approval process; devices go through the medical device pathway. A manufacturer that guesses wrong at the outset can spend years building the wrong kind of application file.

Combination Products

Some products combine a device component with a drug or biological component, and the device definition alone cannot resolve which regulatory track they follow. A drug-eluting coronary stent is the classic example: the stent scaffolds the artery mechanically while releasing a drug to prevent re-narrowing. These are regulated as “combination products,” and the FDA assigns each one a lead review center based on which component provides the most important therapeutic action.

The FDA calls this the “primary mode of action,” or PMOA — the single mode of action expected to make the greatest contribution to the product’s overall therapeutic effect.⁴ If the device function drives the benefit, the Center for Devices and Radiological Health takes the lead. If the drug function dominates, the Center for Drug Evaluation and Research leads instead. Manufacturers who are unsure can file a Request for Designation with the Office of Combination Products to get an official assignment before investing in a submission.⁵

The Clinical Decision Support Software Carve-Out

Software raises its own questions under Section 201(h). A mobile app that monitors blood glucose readings for a diabetic patient fits the device definition cleanly. It is intended to manage disease, and it works through data processing rather than chemistry. But not all health-related software is a device. Congress carved out certain clinical decision support software in Section 520(o)(1)(E) of the FD&C Act. To fall outside the device definition, the software must meet all four of the following criteria:⁶

It is not intended to acquire, process, or analyze a medical image, a signal from an in vitro diagnostic device, or a pattern from a signal acquisition system.
It is intended to display, analyze, or print medical information about a patient or other relevant clinical information such as peer-reviewed studies or clinical practice guidelines.
It is intended to support or provide recommendations to a healthcare professional about prevention, diagnosis, or treatment, rather than issuing a specific directive.
It enables the healthcare professional to independently review the basis for the recommendation, so the professional does not rely primarily on the software’s output for a clinical decision.

Fail any one of those four criteria and the software remains a device. Software designed for time-critical clinical decisions is particularly unlikely to satisfy the independent-review criterion, because a clinician working under emergency conditions cannot realistically pause to evaluate the software’s reasoning before acting on it.

Why the Definition Matters

Section 201(h) is the gateway to the entire device regulatory regime. A product that meets the definition must generally be cleared or approved by the FDA before it can be legally marketed in the United States, and the manufacturer must comply with registration, listing, labeling, quality system, and postmarket reporting requirements. A product that does not meet the definition is not subject to any of that.

Under Section 301 of the FD&C Act, introducing an adulterated or misbranded device into interstate commerce is a prohibited act.⁷ A device is adulterated when, among other things, a Class III device lacks required premarket approval or the device was manufactured in facilities that do not meet applicable quality system requirements.⁸

The penalties are substantial. Civil penalties reach up to $35,466 per violation and up to $2,364,503 for all violations in a single proceeding under the most recent inflation adjustment.⁹ Criminal penalties for a first offense reach up to one year in prison, a fine of up to $1,000, or both. For repeat violations or violations committed with intent to defraud or mislead, the maximum rises to three years in prison, a fine of up to $10,000, or both.⁷ The FDA can also seek injunctions halting all sales and distribution and can seize product already in the market. A first offense does not require intent, which is where manufacturers of wellness products, health-related software, and laboratory instruments most often get caught: their marketing claims quietly create an intended use that brings the product under Section 201(h) before anyone at the company has thought to check.

1
Office of the Law Revision Counsel. 21 USC 321 Definitions Generally
2
U.S. Food and Drug Administration. Classification of Products as Drugs and Devices and Additional Product Classification Issues
3
eCFR. 21 CFR 801.4 – Meaning of Intended Uses
4
Federal Register. Definition of Primary Mode of Action of a Combination Product
5
U.S. Food and Drug Administration. How to Write a Request for Designation RFD
6
U.S. Department of Health and Human Services, Food and Drug Administration. Clinical Decision Support Software – Guidance for Industry and Food and Drug Administration Staff
7
Office of the Law Revision Counsel. 21 USC Chapter 9 Subchapter III – Prohibited Acts and Penalties
8
Office of the Law Revision Counsel. 21 USC 351 Adulterated Drugs and Devices
9
Federal Register. Annual Civil Monetary Penalties Inflation Adjustment