Therapeutic Equivalence Codes: How the FDA Determines If Generic Drugs Can Be Substituted

When you pick up a prescription at the pharmacy, you might not realize that the pill in your hand could be a generic version of the brand-name drug your doctor prescribed. But here’s the real question: can you be sure it will work the same way? That’s where therapeutic equivalence codes come in. These aren’t just letters and numbers on a label-they’re the FDA’s official way of telling pharmacists and doctors which generic drugs can be swapped in without risking your health or treatment outcome.

What therapeutic equivalence really means

This system was created after the Hatch-Waxman Act of 1984, which aimed to speed up access to cheaper generics without compromising safety. Before that, many generics entered the market with little proof they worked like the original. Today, the FDA evaluates every generic drug using strict standards, and assigns a code based on that evaluation. This code appears in the Approved Drug Products with Therapeutic Equivalence Evaluations, commonly called the Orange Book. It’s updated monthly and used daily by pharmacists across the country.

The ABCs of TE codes

• A = Therapeutically equivalent. This is the gold standard. You can substitute this generic without hesitation.
• B = Not yet determined to be equivalent. These need more scrutiny. Don’t assume they’re unsafe-just that the evidence isn’t clear enough for automatic substitution.

But it doesn’t stop there. After the first letter, you’ll often see numbers or extra letters. For example:

• AB = Bioequivalent to the reference drug. This is the most common rating for simple oral tablets.
• AB1, AB2, AB3 = These mean there are multiple brand-name drugs used as reference points. AB1 means it matches the first reference listed, AB2 the second, and so on. If you’re switching between generics, you need to match the AB number.
• BC = Extended-release products with potential bioequivalence issues.
• BT = Topical products (like creams or gels) where skin absorption is hard to measure.
• BN = Inhalers or nebulizer products.
• BX = Not enough data to make a call. These are often new or complex products still under review.

Here’s the key takeaway: Only products with an 'A' code are automatically substitutable under most state laws. If you see a 'B', it doesn’t mean the drug doesn’t work-it means the FDA hasn’t confirmed it’s interchangeable with the brand. That’s why pharmacists double-check before swapping.

Why some generics get 'B' codes-even if they seem identical

For simple tablets, bioequivalence is easy to prove. You give volunteers the brand and the generic, measure blood levels over time, and if the curves match within strict limits, it’s an 'A'. But for complex products-like inhalers, injectables, or topical creams-the body doesn’t absorb the drug the same way. A cream might look identical, but if it doesn’t penetrate the skin at the same rate, it won’t work the same.

That’s why products like corticosteroid creams, insulin inhalers, or certain arthritis injections often get 'B' codes. The FDA doesn’t have reliable tests to prove they’re interchangeable. A 2021 study in the AAPS Journal found that over 60% of topical generics received 'B' ratings, even though they were chemically identical to the brand. This isn’t a flaw in the product-it’s a flaw in the current testing method.

And here’s the catch: some 'B'-rated products may be just as effective. But because the FDA can’t confirm it, pharmacists are legally required to hold off on substitution unless the prescriber says it’s okay. This causes confusion. A 2022 AMA survey showed that 42% of physicians didn’t understand how to interpret 'B' codes. Some refused to let pharmacists substitute them, even when the patient had been stable on the generic for years.

How pharmacists use the Orange Book every day

That might sound like a lot, but it saves time overall. In 2023, the American Pharmacists Association estimated that proper use of TE codes saved the U.S. healthcare system $1.2 billion annually by ensuring the right generics were used without unnecessary brand switches. States have laws that back this up: 49 out of 50 allow pharmacists to substitute 'A'-rated generics without asking the doctor. Only in New York do you need explicit permission for any substitution.

But things get messy with 'B' codes. Thirty-eight states require pharmacists to notify the prescriber if they want to substitute a 'B'-rated product. Some pharmacists will call the doctor. Others will wait for the patient to return with a new prescription. It adds friction-but it’s designed to protect patients.

What the FDA is doing to fix the gaps

In 2022, the FDA released a draft guidance proposing changes. They’re now working on Product-Specific Guidances (PSGs)-over 1,850 as of August 2023-that give manufacturers detailed instructions on how to prove equivalence for each specific drug. These aren’t one-size-fits-all rules. They’re tailored to each medicine’s chemistry and delivery method.

The goal? Reduce 'B' ratings for complex generics by 30% by 2027. That means more accurate codes, fewer unnecessary restrictions, and more access to affordable alternatives. The FDA is also exploring real-world data-like patient outcomes from electronic health records-to supplement lab tests. If a generic has been used safely by thousands of patients for years, maybe that’s evidence enough.

What this means for you as a patient

But if you’re prescribed a 'B'-rated product, ask your doctor: Is this the only option? Is there an 'A'-rated alternative? Some patients end up paying more because their prescriber doesn’t realize a cheaper, equivalent option exists. On the flip side, if you’ve been on a 'B'-rated drug for months with no issues, don’t assume it’s unsafe. Sometimes, the code reflects a lack of testing-not a lack of safety.

The bottom line: therapeutic equivalence codes exist to give you access to affordable drugs without compromising your care. They’re not perfect, but they’re the best system we have. And they’re getting better.