Biosimilar Interchangeability Checker
Check FDA-Approved Interchangeable Biosimilars
The Purple Book is the FDA's official database for biologic drugs and biosimilars. Search for your drug to see if it has FDA-approved interchangeable biosimilars.
The Purple Book isn’t a book you can hold. It’s a live, searchable database run by the U.S. Food and Drug Administration (FDA) that tells you which biological drugs are approved, which ones are biosimilars, and which ones can actually be swapped out at the pharmacy like generic pills. If you’re a pharmacist, a doctor, or even a patient trying to understand why your insulin or arthritis drug suddenly has a different name but the same price, this is the resource that explains it all.
What Exactly Is the Purple Book?
Launched in 2012 as part of the Biologics Price Competition and Innovation Act (BPCIA), the Purple Book started as two separate lists-one for drugs handled by the Center for Drug Evaluation and Research (CDER), another for those under the Center for Biologics Evaluation and Research (CBER). But in 2020, the FDA merged them into one clean, searchable system. Today, it’s the go-to source for anyone needing to know if a biological product is approved, if it’s a biosimilar, or if it’s interchangeable.
Think of it like a digital catalog, but instead of listing books, it lists complex medicines made from living cells-things like insulin, rheumatoid arthritis treatments, cancer drugs, and vaccines. Each entry includes the brand name, the generic name, when it was approved, and whether it’s a reference product, a biosimilar, or an interchangeable product.
Biosimilars vs. Interchangeable Products: The Difference That Matters
Here’s where things get tricky. Not all biosimilars are the same. All interchangeable products are biosimilars, but not all biosimilars can be swapped at the pharmacy.
A biosimilar is a biological product that’s extremely similar to an already-approved reference product. The FDA says there are no clinically meaningful differences in safety, purity, or potency. That means if you’re on Humira, and your doctor switches you to a biosimilar version, it should work just as well. But here’s the catch: a biosimilar alone doesn’t let a pharmacist automatically substitute it for the brand name drug.
An interchangeable product goes further. To earn that label, the FDA requires extra proof: switching back and forth between the biosimilar and the original product doesn’t increase risk or reduce effectiveness. That means if a patient uses the brand drug for a month, then switches to the biosimilar for a month, then switches back, their body responds the same way every time. No drop in results. No spike in side effects.
That’s why interchangeability matters. It’s not about being better. It’s about being predictable. The FDA makes it clear: an interchangeable designation doesn’t mean the product is safer or more effective-it just means you can switch between them without worrying about unintended consequences.
How the Purple Book Shows You What’s What
The Purple Book doesn’t just list products. It groups them smartly. When you search for Humira, you’ll see its original listing-and underneath it, all the biosimilars and interchangeable versions that have been approved to match it. Each one has a matching color on its product card so you can instantly tell which ones are linked.
Each product card also shows icons for how the drug is delivered-autoinjector, pre-filled syringe, vial-so pharmacists and patients know what to expect. The date of approval, whether it’s covered by exclusivity, and its regulatory path (351(a), 351(k) biosimilar, or 351(k) interchangeable) are all clearly labeled.
For example, if you search for “insulin glargine,” you’ll see multiple entries. One might say “Lantus (reference),” and below it, two biosimilars, and one marked “interchangeable.” That one can be swapped without asking the doctor-depending on your state’s rules.
Why State Laws Change Everything
Even if the FDA says a biosimilar is interchangeable, that doesn’t mean every pharmacy will automatically swap it. Each state has its own rules.
As of 2023, 47 states and Puerto Rico allow pharmacists to substitute an interchangeable biosimilar without contacting the prescriber. But in those states, some still require the pharmacist to notify the doctor, document the swap, or tell the patient. A few states still require explicit permission from the prescriber every time.
This creates a patchwork. A patient in New York might get an interchangeable biosimilar without knowing. A patient in California might get the same drug, but only after the pharmacist calls the doctor. And in states that don’t allow substitution at all, even an FDA-approved interchangeable product stays on the shelf.
That’s why the Purple Book doesn’t tell you what you can get-it tells you what’s approved. The rest? That’s up to your state pharmacy board.
What’s Approved So Far?
As of late 2023, only seven biosimilars had earned the interchangeable designation from the FDA. That might sound low, but it’s growing fast.
Two of them are insulin products-critical for people with diabetes who need consistent, affordable options. Three treat inflammatory conditions like rheumatoid arthritis and Crohn’s disease. Two are for eye conditions in patients with diabetic retinopathy.
These aren’t experimental. They’re all based on well-established reference products with decades of safety data. The FDA didn’t approve them lightly. Each one went through multiple clinical trials showing that switching back and forth didn’t hurt patients.
Companies are now filing more applications. More interchangeable biosimilars are expected in the next 12-18 months, especially for popular drugs like adalimumab and etanercept.
What the Purple Book Doesn’t Tell You
The Purple Book is a regulatory tool, not a clinical guide. It won’t tell you which drug is cheaper. It won’t tell you if your insurance covers it. It won’t explain side effects in plain language.
It also doesn’t distinguish between “unbranded biologics” and interchangeable biosimilars. The FDA calls unbranded biologics “equivalent” to the brand name, but they’re not interchangeable under federal law. That’s a gray area that even some pharmacists get confused about.
And while the database is searchable and updated daily, it doesn’t include products that are pending approval or under review. If you’re looking for a biosimilar that’s not listed yet, it’s not because the FDA hid it-it’s because it hasn’t been approved.
Who Uses the Purple Book-and Why?
Pharmacists rely on it daily to decide if they can substitute a drug. Prescribers use it to understand what options are available when writing new prescriptions. Patients can use it to check if their medication has a cheaper, FDA-approved alternative.
Insurance companies use it to update their formularies. Policymakers use it to shape state laws. Researchers use it to track how many biosimilars are entering the market.
It’s not marketing. It’s not opinion. It’s the official, factual record of what the FDA has approved-and that’s rare in healthcare.
Where to Find It
The Purple Book is free, online, and updated daily. Go to fda.gov, search for “Purple Book,” and you’ll land on the official page. You can search by brand name, generic name, or manufacturer. You can filter by product type-insulin, autoimmune, oncology-and see only the interchangeable products.
The FDA even has a short video walkthrough that shows you how to use it. No login. No fee. No subscription. Just clear, accurate data.
And unlike older versions, it’s now a single, unified database. No more flipping between two separate lists. No more confusion.
What’s Next?
The FDA is working on clearer labeling rules for biosimilars and interchangeable products. That means future product cards will be even easier to read. More companies are investing in switching studies to earn interchangeability status. As costs keep falling, more patients will gain access to these drugs.
But the real shift isn’t just in the science. It’s in the system. The Purple Book is helping turn biological drugs from exclusive, high-cost products into ones that can be competed with, substituted, and made affordable.
That’s the goal of the BPCIA. And the Purple Book? It’s the tool making it real.
Is the Purple Book the same as the Orange Book?
No. The Orange Book lists approved generic chemical drugs and their patent status. The Purple Book does the same thing-but for biological products, including biosimilars and interchangeable products. They’re two separate systems for two different kinds of medicines.
Can a pharmacist substitute a biosimilar without telling me?
Only if it’s an FDA-approved interchangeable product AND your state allows substitution without prescriber permission. Even then, some states require the pharmacist to notify your doctor or document the swap. Always ask your pharmacist if substitution happened.
Are interchangeable biosimilars safer than regular biosimilars?
No. The FDA says interchangeability doesn’t mean a product is safer or more effective. It just means switching between it and the original drug won’t cause unexpected changes in safety or effectiveness. Both types are held to the same high standard for similarity.
Why aren’t there more interchangeable biosimilars on the market?
Because proving interchangeability takes more time and money. Companies need to run additional clinical studies showing that switching back and forth between the biosimilar and the brand drug doesn’t change outcomes. That’s harder and costlier than proving basic biosimilarity. Many companies are working on it, but it’s a slower process.
Can I use the Purple Book to find cheaper alternatives to my biologic?
Yes. Search your brand-name biologic in the Purple Book. If you see one or more biosimilars listed under it, those are FDA-approved alternatives. If one is marked “interchangeable,” it may be automatically substitutable in your state. Talk to your pharmacist or doctor to see if switching is right for you.