Biosimilar Substitution Checker
Check Product Status
How This Works
The Purple Book shows whether a biological product is a reference product, biosimilar, or interchangeable.
Reference Product - The original drug that others are compared to
Biosimilar - Similar to reference product but requires prescriber approval for substitution
Interchangeable - Can be substituted without prescriber intervention (if allowed by state law)
Search Results
Enter a product name to check its status
Important Considerations
Interchangeable products can be substituted without prescriber approval only if state law allows it. As of 2023, 47 states and Puerto Rico allow pharmacist substitution for interchangeable products.
The FDA only designates products as interchangeable. State laws determine if substitution is allowed. Check your state's pharmacy board rules for specific requirements.
The Purple Book is the U.S. Food and Drug Administration’s official database for biological products, including biosimilars and interchangeable biologics. It’s not a physical book-it’s a live, searchable online tool that helps pharmacists, doctors, and patients understand which biological medicines are approved, which ones can be swapped out, and why. This matters because biological drugs are complex, expensive, and often life-changing. When a biosimilar enters the market, it can lower costs. But only if it’s labeled as interchangeable can a pharmacist automatically substitute it without asking the prescriber. The Purple Book tells you which ones qualify.
What’s in the Purple Book?
The Purple Book lists every FDA-licensed biological product regulated by the Center for Drug Evaluation and Research (CDER) and the Center for Biologics Evaluation and Research (CBER). That includes everything from insulin and rheumatoid arthritis treatments to vaccines and gene therapies. Each entry shows the product’s approval date, whether it’s a reference product (the original), a biosimilar, or an interchangeable product.
Here’s how it works visually: products with the same color card belong to the same family. If you search for Humira, you’ll see the original drug and all its biosimilars grouped under it. The color-coding makes it easy to spot which biosimilars are linked to which reference product. You’ll also see icons that show how the drug is delivered-like autoinjectors or pre-filled syringes-which helps pharmacists match the right product to the patient’s needs.
The database was updated in 2020 to merge two older lists into one searchable system. Before that, finding information was messy. Now, you can type in a brand name, a generic name, or even a manufacturer, and get clear results. The FDA says this was done specifically to help pharmacists make fast, confident decisions at the counter.
Biosimilar vs. Interchangeable: The Key Difference
Not all biosimilars are created equal. Every interchangeable product is a biosimilar, but not every biosimilar is interchangeable. That’s the core distinction.
A biosimilar is a biological product that’s highly similar to its reference product. The FDA requires proof that there are no clinically meaningful differences in safety, purity, or potency. That means the drug works the same way, has the same side effects, and delivers the same results. But here’s the catch: biosimilars don’t automatically replace the original drug in the pharmacy. A pharmacist still needs permission from the prescriber to swap them.
An interchangeable product goes further. To earn that label, the manufacturer must prove that switching back and forth between the biosimilar and the original drug won’t increase risk or reduce effectiveness. That requires real-world clinical studies where patients are switched multiple times-sometimes between the biosimilar and the reference product-to prove stability and consistency. The FDA doesn’t say interchangeable biologics are better. They’re just proven to be reliably swappable.
For example, if a patient is on Enbrel and their pharmacist has an interchangeable biosimilar on hand, they can switch without calling the doctor. That’s only allowed if the product is marked as interchangeable in the Purple Book. Without that designation, even if it’s a biosimilar, the pharmacist must wait for the prescriber’s okay.
Why Does Interchangeability Matter?
It comes down to access and cost. Biological drugs can cost over $20,000 a year. Biosimilars cut that price by 15% to 35%. But if pharmacists can’t substitute them automatically, many patients never get the savings.
Interchangeable products remove the friction. No extra paperwork. No delay. No need to contact the doctor. That’s huge for patients on chronic treatments-like diabetes, Crohn’s, or rheumatoid arthritis-who need consistent, uninterrupted access to their medicine.
As of November 2023, only seven biosimilars had earned the interchangeable designation from the FDA. Two are insulins. Three treat inflammatory conditions. Two are for eye diseases. That number is growing, but slowly. Why? Because the data needed to prove interchangeability is expensive and complex. Manufacturers have to run switching studies with hundreds of patients over months, sometimes years.
And here’s something important: the FDA is clear. An interchangeable designation doesn’t mean the product is safer or more effective. It just means you can switch between it and the original without worrying about side effects or loss of benefit. That’s a big deal for pharmacy systems and insurance plans trying to drive down costs.
State Laws Change the Game
The FDA says a product is interchangeable. But whether a pharmacist can actually swap it depends on where you live.
As of 2023, 47 states and Puerto Rico allow pharmacists to substitute an interchangeable biosimilar without contacting the prescriber. That’s great-but not universal. In the remaining states, pharmacists must notify the doctor, get approval, or document the switch. Some states even require the patient to be informed in writing.
This patchwork of rules creates real confusion. A patient in New York might get a substitution automatically. The same patient in California might not. A pharmacy chain with locations across multiple states has to train staff differently in each one. It’s inefficient. It’s frustrating. And it slows down cost savings.
The FDA’s Purple Book doesn’t track state laws. It only shows federal approval. So pharmacists have to check their state’s pharmacy board rules separately. That’s why many still default to the original drug unless they’re absolutely sure.
What’s Next for the Purple Book?
The FDA is working on clearer labeling rules for biosimilars and interchangeable products. Draft guidance released in 2023 aims to make product names and packaging less confusing. Right now, some biosimilars have very similar names to the originals, which can lead to errors. The FDA wants to fix that.
More interchangeable products are expected in 2025 and 2026. Companies are actively applying. Insulin, monoclonal antibodies for autoimmune diseases, and even some cancer treatments are on the pipeline. As more get approved, the Purple Book will become even more essential.
But adoption isn’t just about approval. It’s about education. Pharmacists need to know how to use the database. Prescribers need to understand what interchangeability means. Patients need to know they can ask for a biosimilar if it’s available. The Purple Book is a tool. But its power only comes when people know how to use it.
How to Use the Purple Book
It’s free. It’s online. And it’s updated regularly. Here’s how to use it:
- Go to the FDA’s Purple Book page.
- Use the search bar to look up a brand name, generic name, or manufacturer.
- Look for the product card. Color matches show related products.
- Check the designation: 351(a) = reference product; 351(k) Biosimilar; 351(k) Interchangeable.
- Click on the product to see its approval date, exclusivity status, and whether it’s interchangeable.
There’s also a downloadable version for offline use, and the FDA offers a video walkthrough that shows exactly how to navigate the system. No login. No fee. Just direct access to the facts.
| Feature | Biosimilar | Interchangeable |
|---|---|---|
| Definition | Highly similar to reference product with no clinically meaningful differences | Biosimilar that can be substituted without prescriber intervention |
| Approval Requirements | Analytical, nonclinical, and clinical data showing similarity | All biosimilar data + switching studies proving safety and efficacy on repeated alternation |
| Substitution by Pharmacist | Not allowed without prescriber permission | Allowed if permitted by state law |
| Number Approved (as of 2023) | Over 30 | 7 |
| Primary Purpose | Cost reduction through competition | Seamless substitution to improve access and adherence |
Frequently Asked Questions
Is the Purple Book only for pharmacists?
No. While pharmacists use it most often to decide on substitutions, doctors, insurers, patients, and even researchers rely on the Purple Book. It’s the only official source that tells you which biological products are interchangeable. Anyone involved in prescribing, dispensing, or paying for biologics should know how to use it.
Can a biosimilar be switched to another biosimilar?
The FDA hasn’t approved switching between biosimilars. The interchangeability designation only applies between a biosimilar and its reference product. If a patient is on one biosimilar and wants to switch to another, the prescriber must make that decision. There’s no data yet proving it’s safe to switch from one biosimilar to another.
Why aren’t more products labeled as interchangeable?
Because the evidence required is harder and more expensive to gather. Companies must run switching studies with real patients, showing that alternating between the biosimilar and the original doesn’t increase risk. That takes time, money, and large clinical trials. Many manufacturers are still working on it, but it’s not a priority for all.
Does the FDA approve interchangeable products faster?
No. The approval process is the same length. The difference is in the data submitted. A biosimilar application includes similarity data. An interchangeable application adds switching data. The FDA reviews both the same way-just with more information to evaluate. The timeline doesn’t change.
What happens if a state bans substitution?
Even if a product is federally designated as interchangeable, the pharmacist can’t substitute it in states that don’t allow it. State law overrides federal designation in this case. Pharmacists must follow their state’s pharmacy board rules. That’s why knowing your state’s laws is as important as knowing the Purple Book.
What Should You Do Next?
If you’re a pharmacist: Bookmark the Purple Book. Print the guide. Train your team. Make sure everyone knows how to find interchangeable products.
If you’re a prescriber: Talk to your pharmacy. Ask which biosimilars are interchangeable in your area. Encourage patients to ask about cost-saving options.
If you’re a patient: Ask if there’s a biosimilar version of your drug. If it’s interchangeable, ask if you can switch. You’re entitled to know your options.
The Purple Book isn’t magic. But it’s the most powerful tool we have to make biological medicines more accessible, affordable, and easier to use. The science is solid. The data is clear. Now it’s up to the system to catch up.
