FDA Finalizes Rules for Deciding When Generic Drugs Can Substitute for Brand-Name Prescriptions

The U.S. Food and Drug Administration has finalized guidance explaining how it determines whether prescription drug products are therapeutically equivalent—an evaluation that can help pharmacists, prescribers and state agencies determine when an approved generic can be substituted for another version of the same drug.

The FDA announced the final “Evaluation of Therapeutic Equivalence” guidance in August 2026, completing a process that began with draft guidance issued in July 2022. The agency says the document explains its current thinking about therapeutic equivalence evaluations and the codes used to communicate those determinations.

For patients, the technical-sounding guidance helps explain something that happens every day at pharmacy counters: how FDA determines that certain approved drug products can be expected to provide the same clinical effect and safety profile when substituted appropriately.

What Does “Therapeutically Equivalent” Actually Mean?

FDA doesn’t consider two prescription drugs therapeutically equivalent simply because they contain an ingredient with the same name.

According to the agency’s current Orange Book guidance, therapeutically equivalent products generally must be approved as safe and effective, be pharmaceutical equivalents, meet applicable standards for strength, quality, purity and identity, and satisfy bioequivalence requirements. They also must be adequately labeled and manufactured in compliance with Current Good Manufacturing Practice requirements.

When FDA classifies drug products as therapeutically equivalent, the agency says they can be expected to produce the same clinical effect and safety profile when used under the conditions specified in their labeling.

That does not mean two products necessarily look identical. Therapeutically equivalent products can have differences involving color, shape, packaging, scoring, inactive ingredients and other characteristics.

The Orange Book Is Where FDA Records These Evaluations

FDA publishes therapeutic equivalence evaluations in its resource officially titled Approved Drug Products With Therapeutic Equivalence Evaluations, better known as the Orange Book.

The FDA Orange Book contains approved drug products along with therapeutic equivalence information for applicable multisource prescription drugs. Users can search by active ingredient, proprietary name, applicant, application number, dosage form and other criteria.

FDA says these evaluations are intended to provide information and advice to state health agencies, prescribers and pharmacists, promote education about drug selection and help contain healthcare costs.

The electronic Orange Book is also regularly updated. FDA says information on newly approved generics has been updated daily since 2005, while broader files and website updates generally occur monthly.

Those Two-Letter Codes Have an Important Meaning

One practical piece of the system is FDA’s therapeutic equivalence, or TE, code.

Generally, the first letter tells users whether FDA considers products therapeutically equivalent to other pharmaceutically equivalent products. An “A” rating indicates products FDA considers therapeutically equivalent, while a “B” rating identifies products FDA does not currently consider therapeutically equivalent to other pharmaceutically equivalent products.

The second letter provides more information about the agency’s evaluation. For example, an AB rating can be assigned when an actual or potential bioequivalence issue has been resolved through adequate scientific evidence supporting bioequivalence.

That makes the Orange Book considerably more than a list of generic drug names. It gives pharmacists and other healthcare professionals a standardized way to see FDA’s scientific evaluation of substitutability.

Therapeutic Equivalence Doesn’t Mean Every Detail Is Identical

Patients sometimes become concerned when a refill suddenly has a different color, shape or marking than the medication they received the previous month.

FDA explains that therapeutically equivalent products can differ in characteristics that are not required to be identical, including shape, scoring configuration, packaging, certain inactive ingredients, expiration information and sometimes labeling.

Those differences can occasionally matter for individual patients. FDA specifically notes that differences in coloring or preservatives can, in rare situations, contribute to patient-specific allergic reactions, and differences in appearance can create confusion.

Anyone who receives a prescription that looks unexpectedly different should verify the medication with the pharmacist rather than stopping it or changing how it is taken on their own.

Why Generic Substitution Can Matter for Prescription Costs

Therapeutic equivalence evaluations have an important economic purpose as well. FDA explicitly identifies containing healthcare costs as one of the goals behind making these evaluations available to health agencies, prescribers and pharmacists.

Generics can give consumers additional options when multiple manufacturers offer versions of the same prescription drug. However, therapeutic equivalence does not guarantee that every generic will have the same retail price, copayment or insurance coverage.

Patients with Medicare Part D or private insurance should still check their specific plan’s formulary and pharmacy pricing when costs matter. The FDA’s determination addresses whether applicable drug products are therapeutically equivalent; it does not determine what an individual insurance plan will charge a patient.

The New Guidance Doesn’t Change a Specific Prescription Overnight

Importantly, FDA’s August announcement is guidance about how the agency evaluates therapeutic equivalence rather than a notice changing the status of one particular medication.

The final document replaces the draft guidance issued in July 2022 and establishes FDA’s current thinking on therapeutic equivalence evaluations and TE codes.

Patients therefore should not interpret the announcement as meaning their current generic medication has suddenly changed or that a particular brand-name prescription must now be replaced.

Anyone curious about a particular drug can search FDA’s Orange Book and discuss the results with a pharmacist or prescriber. Professional judgment remains important, and FDA specifically notes that its therapeutic equivalence evaluations do not relieve healthcare professionals of their responsibilities when prescribing and dispensing medication for individual patients.

What to Read Next

FDA Eases Approval Path for Certain Cancer Companion Diagnostic Tests

8 Over-the-Counter Drugs the FDA Just Flagged as Dangerous for Anyone Over 60

FDA “Class I” Alert: The 3 Specific Beverage Mixes Seniors Should Throw Away Immediately This Weekend

Amanda Blankenship

Amanda Blankenship is Chief Editor at District Media, Inc., leading content strategy, quality assurance, and editorial operations across high-traffic personal finance sites like SavingAdvice.com and CleverDude.com. A Wingate University graduate with a BA in Communications (Journalism focus), she brings over a decade of experience in digital publishing, writing, and team leadership in the personal finance space.