AB and B Codes: What They Mean and How They Affect Your Medications

When you pick up a generic prescription, you might not realize there’s a hidden code on the label that could make the difference between safe treatment and serious risk. These are the AB and B codes, FDA-assigned ratings that determine if a generic drug is therapeutically equivalent to its brand-name version. Also known as therapeutic equivalence codes, they’re not just paperwork—they directly impact whether your medication will work the same way, every time. If you’re on a drug with a narrow therapeutic index—like warfarin, levothyroxine, or phenytoin—getting the wrong code could mean your blood levels swing dangerously high or low. That’s why understanding these codes isn’t optional. It’s essential.

These codes come from the FDA’s Orange Book, the official database that lists approved drug products with therapeutic equivalence evaluations. Also known as Therapeutic Equivalence Evaluations, it’s the backbone of how pharmacies and insurers decide which generics to substitute. An AB rating means the generic has been proven bioequivalent: same active ingredient, same dose, same absorption rate, and same clinical effect. That’s the gold standard. But a B code? That’s a red flag. It means the generic hasn’t met the FDA’s strict bioequivalence standards. It might look the same, but your body could process it differently. This isn’t theoretical. People on generic NTI drugs have ended up in the hospital because a B-rated substitute changed their blood levels just enough to cause toxicity or treatment failure.

It’s not just about the code itself—it’s about how it connects to the drugs you take. If you’re on metoclopramide, you need to know if the generic you’re getting has the same absorption profile. If you’re taking methotrexate, even small differences in how the drug enters your bloodstream can increase side effects. The same goes for statins and grapefruit interactions, or blood pressure meds like valsartan-hydrochlorothiazide that were recently recalled. These aren’t random issues—they’re all tied to how well a generic version matches the original. That’s why the Orange Book matters. It’s the only place where you can check if your generic is truly interchangeable.

Most people never look at these codes. Pharmacies assume you’re fine with substitution. Insurance companies push generics to save money. But if you’re on a drug where small changes can cause big problems, you need to ask. Always check the label. Ask your pharmacist: "Is this AB-rated?" If it’s not, push back. There are often multiple generic versions available—some with AB ratings, others with B. You have the right to choose the safer option. And if your doctor doesn’t know about these codes, it’s time they did. This isn’t about being difficult. It’s about making sure your treatment works, not just looks the same.

Below, you’ll find real-world guides that connect directly to these issues—from how to spot unsafe generic switches in your blood pressure meds, to why some NTI drugs need therapeutic drug monitoring, to how recalls like the one for Valsartan-Hydrochlorothiazide can affect you. These aren’t abstract topics. They’re about your health, your safety, and the quiet details most people never think to ask about. Let’s make sure you’re not one of them.