Biosimilar Switching: What Happens When You Change From Originator

When you’ve been on a biologic drug like infliximab or adalimumab for years, your body knows the medicine. It works. You feel stable. Then your doctor says, "We’re switching you to a biosimilar." Suddenly, your mind races: What happens when you change from originator? Will your symptoms come back? Will you feel worse? Is this just a cost-cutting move disguised as medical advice?

What Exactly Is a Biosimilar?

A biosimilar isn’t a generic. That’s the first thing to understand. Generics are exact chemical copies of small-molecule drugs-like taking a different brand of ibuprofen. Biosimilars are copies of complex biologic drugs, which are made from living cells. Think of it like trying to recreate a handmade sweater. Even if you use the same yarn and pattern, the texture, drape, and feel might be slightly different. But if it keeps you warm just as well, does it matter?

The U.S. Food and Drug Administration (FDA) and European Medicines Agency (EMA) require biosimilars to show no clinically meaningful difference in safety, purity, or potency compared to the original. That means the same effectiveness, same side effect profile, same dosing. They’re not identical-no two batches of a biologic are-but they’re close enough that your body responds the same way.

The first biosimilar approved in the U.S. was Zarxio (filgrastim-sndz) in 2015. Since then, 37 biosimilars have been approved, mostly targeting common conditions like rheumatoid arthritis, psoriasis, and inflammatory bowel disease. By 2023, about 70% of all biosimilar use in the U.S. was for tumor necrosis factor (TNF) inhibitors like infliximab and adalimumab.

What Happens When You Switch?

Switching from an originator biologic to a biosimilar isn’t a leap into the unknown. It’s backed by data from over 80 clinical studies. The NOR-Switch trial, which followed 481 patients with inflammatory diseases for a year, found that switching from originator infliximab to its biosimilar CT-P13 resulted in similar disease control. Retention rates were 52.6% for the biosimilar group versus 60% for the originator group-but the difference wasn’t statistically significant. In other words, most people stayed on the treatment without problems.

Real-world data from Denmark, Germany, and the U.S. consistently show that over 85% of patients remain on their biosimilar after 12 months. That’s the same retention rate as staying on the original drug.

One key finding: switching doesn’t cause more side effects. In a 2022 study of 140 patients who switched multiple times-from originator to biosimilar to another biosimilar-immunogenicity (the body making antibodies against the drug) stayed low: only 3 cases per 100 patient-years. Trough levels (the amount of drug left in your blood between doses) didn’t change meaningfully. One patient’s infliximab level went from 4.3 μg/mL to 4.1 μg/mL after switching. That’s a drop of less than 5%. Not clinically relevant.

Why Do Some People Stop Taking It?

Here’s the real issue: people stop not because the drug stops working, but because they think it will.

A 2021 study in Frontiers in Psychology found that 32.7% of patients reported new or worsening symptoms after switching-even though lab tests and disease scores showed no change. This is called the nocebo effect: expecting something bad to happen makes you feel it.

Reddit threads from patients with rheumatoid arthritis are full of posts like: “I switched to the biosimilar and suddenly I’m more tired. My joints ache again.” But when doctors checked their DAS28 scores (a standard measure of RA activity), everything was stable. Same with IBD patients who say, “My stools aren’t normal anymore.” Their fecal calprotectin levels? Still in remission range.

Actual discontinuation due to real drug failure is rare. In studies, only 1.7% of patients stopped because of confirmed immunogenicity. Most stops-12% to 18%-are linked to perception, fear, or poor communication.

Who Shouldn’t Switch?

Switching works best for people with stable disease. If your RA is under control (DAS28 under 3.2), your IBD is in remission, and your psoriasis has cleared up-switching is safe and supported by guidelines from the FDA and EMA.

But if you’re in the middle of a flare, or your disease is unpredictable, don’t switch. That’s not because biosimilars are riskier-it’s because changing anything during a flare makes it impossible to tell if the flare is from the disease or the switch.

Also, avoid multiple switches. Switching once-from originator to biosimilar-is well-studied. Switching twice or three times? The data is thinner. One Spanish study found 15.3% of IBD patients stopped after switching from one biosimilar to another, compared to 8.7% in those who didn’t switch. Trough levels were fine, but something about the change triggered discontinuation. Maybe it’s the uncertainty. Maybe it’s the lack of trust.

The Cost Difference Matters

Biosimilars cost 15% to 35% less than the original biologic. In 2023, when Humira biosimilars hit the U.S. market, they launched at a 35% discount. That’s billions saved for insurers and patients.

In Europe, 67% of filgrastim use is biosimilar. In the U.S., it’s only 24% for infliximab. Why? Patent thickets, rebate deals, and pharmacy networks that favor originators. But health plans are catching on. By 2023, 85% of U.S. health plans had mandatory switch policies for certain biologics.

That’s not just corporate cost-cutting. It’s about access. Many patients can’t afford the originator. A biosimilar makes treatment possible.

What Should You Do Before Switching?

Don’t just accept the switch. Ask for a conversation. A good provider will spend at least 20 minutes explaining:

• Why you’re switching
• What the biosimilar is (and isn’t)
• What to expect-both good and bad
• How you’ll be monitored (DAS28, PASI, trough levels, etc.)
• When to call if you feel off

The PERFUSE study showed that with this kind of education, discontinuation dropped from 18% to just 6.4%. That’s a 64% reduction in people stopping treatment-just by talking.

Ask for a baseline test before switching: trough level, antibody screen, disease activity score. Then repeat it at 3 months. That way, if something changes, you’ll know if it’s the drug or the disease.

Interchangeability: The Next Step

In 2024, the FDA approved the first interchangeable adalimumab biosimilar: Cyltezo. That means pharmacists can swap it for the originator without asking your doctor. It’s like switching from brand-name Advil to generic ibuprofen-but for a complex biologic.

This is huge. It means easier access, less paperwork, lower cost. But it also means less control. Some patients worry about being switched without their knowledge. That’s why clear communication before the switch matters more than ever.

Bottom Line

Switching from an originator biologic to a biosimilar is safe for most people with stable chronic disease. The science says so. The real-world data says so. The regulatory agencies say so.

The biggest risk isn’t the drug. It’s fear. Misinformation. Poor communication.

If you’re being asked to switch, don’t panic. Ask questions. Get data. Know what’s normal. Track how you feel. And remember: you’re not being replaced. You’re being given the same effective treatment at a lower cost.

The goal isn’t to switch everyone. It’s to make life-changing treatments available to everyone. And that’s worth getting right.