When you’ve been on a biologic drug for years-maybe infliximab or adalimumab-to manage rheumatoid arthritis, Crohn’s disease, or psoriasis, your body gets used to it. You know how it feels when your joints stop aching, when your skin clears up, when you can finally walk without pain. Then your doctor says, "We’re switching you to a biosimilar." And suddenly, you’re not sure what that even means. Is it the same? Will it work? What if something goes wrong?
What Exactly Is a Biosimilar?
A biosimilar isn’t a generic. That’s the first thing to understand. Generics are exact copies of small-molecule drugs like aspirin or metformin. Biosimilars are copies of complex biological drugs made from living cells-like proteins, antibodies, or vaccines. Because they come from living systems, they can’t be identical. But they don’t need to be. The U.S. FDA and the European Medicines Agency (EMA) require biosimilars to show no clinically meaningful differences in safety, purity, or potency compared to the original drug, called the originator.Think of it like two different brands of whole milk. One comes from a farm in Wisconsin, another from a cooperative in Australia. They’re not the same cow, not the same feed, not the same packaging. But both have the same fat content, same vitamins, same nutritional value. You wouldn’t expect one to give you a stomachache and the other not. That’s the standard for biosimilars.
The first biosimilar approved in the U.S. was Zarxio (filgrastim-sndz) in 2015. Since then, 37 have been approved, mostly targeting TNF inhibitors like infliximab and adalimumab. These are the most commonly used biologics for autoimmune diseases. By 2023, over 70% of all biosimilar use in the U.S. involved these drugs.
What Happens When You Switch?
Switching means stopping your originator biologic and starting a biosimilar. It can happen for two reasons: medical or non-medical. Medical switching is when your doctor decides it’s better for your condition-maybe your current drug isn’t working well anymore. Non-medical switching is when your insurance, pharmacy, or healthcare system forces the change to save money. That’s the more common-and more controversial-scenario.Studies show that in stable patients, switching works. The NOR-Switch study in Norway followed 481 people with inflammatory arthritis or IBD who switched from originator infliximab to the biosimilar CT-P13. After one year, 52.6% stayed on the biosimilar. The group that stayed on the originator? 60%. That difference wasn’t statistically significant. In other words, the switch didn’t cause more people to stop treatment.
Another study tracked 140 patients who switched from originator infliximab to CT-P13, then to another biosimilar, SB2. Over time, their antibody levels stayed low. Trough levels-the amount of drug in the blood-didn’t change. Side effects? No increase. This was published in Scientific Reports in 2022. Multiple switches didn’t make things worse.
Even in IBD, where keeping inflammation under control is critical, switching from one biosimilar to another (like CT-P13 to SB2) didn’t trigger flares. A 2021 study showed 90.6% of patients stayed in remission. Fecal calprotectin, a marker of gut inflammation, stayed nearly identical before and after the switch.
Why Do Some People Stop?
If the science says it’s safe, why do some people quit? The answer isn’t always medical.One major factor is the nocebo effect. That’s the opposite of placebo. Instead of expecting to feel better, you expect to feel worse. And your body responds accordingly. A 2021 study in Frontiers in Psychology found that 32.7% of patients reported new symptoms-joint pain, fatigue, rashes-after switching, even though lab tests showed no change in disease activity. They felt different. So they stopped.
Reddit threads from patients with rheumatoid arthritis are full of stories: "I switched and my knees locked up." "I had a rash I never had before." "I just didn’t feel right." But when doctors checked their DAS28 scores (a standard measure of RA activity), most were unchanged. The symptoms were real to them-but not caused by the drug itself.
Actual side effects from biosimilars are rare. In one large study, only 1.7 immunogenicity-related events happened per 100 patient-years. That’s less than 2% over a year. Injection site reactions? A bit more common-about 7.8% in adalimumab biosimilar users-but still not high.
Then there’s the psychological side. If you’ve been on Humira for five years, it’s not just a drug. It’s part of your identity. You know how it makes you feel. You trust it. Switching feels like losing control. And when you’re told, "You have to switch," it can feel like a punishment, not a benefit.
Cost and Access: The Real Reason for Switching
Biosimilars cost 15% to 35% less than originators. In 2023, when Humira biosimilars hit the U.S. market, they launched at a 35% discount. That’s huge. Health plans are under pressure to cut costs. By 2023, 85% of U.S. health plans had mandatory switch policies for certain biologics.Europe leads the world in biosimilar adoption. In countries like Sweden and Germany, over 60% of patients on filgrastim are on biosimilars. In the U.S., adoption is slower-only 24% for infliximab-because of patent thickets, rebate deals, and pharmacy benefit managers who profit from keeping originators in place.
But the math is simple: if you save $10,000 per patient per year on one drug, and you have 1,000 patients, that’s $10 million saved. That money can fund other treatments, hire more nurses, expand access to care. For many patients, especially those without good insurance, biosimilars are the only way they can afford to stay on treatment at all.
When Switching Might Not Be Safe
Not everyone is a good candidate. If you’re in a flare, if your disease is active, if your DAS28 score is above 3.2, switching isn’t recommended. The same goes if you’ve had a serious reaction to the originator, or if you’re pregnant or planning to be. Stability matters.Switching between biosimilars-say, from CT-P13 to SB2-is still being studied. Most data is reassuring, but a 2022 Spanish study found a higher discontinuation rate (15.3%) after switching biosimilar to biosimilar in IBD patients compared to historical controls. The reason? No clear clinical reason. Trough levels were fine. Antibodies didn’t spike. But some patients still stopped.
Experts agree: switching once-from originator to biosimilar-is safe. Switching twice or more? Still appears safe, but the data is thinner. The NOR-SWITCH II extension showed 89.2% retention after two years of multiple switches. That’s promising. But we’re still learning.
How to Make the Switch Work
If you’re being switched, here’s what helps:- Ask for a conversation. Don’t just accept the change. Ask your doctor: "Why now? What’s the plan? What if I feel worse?"
- Get baseline data. Before switching, make sure your disease activity is measured-DAS28 for RA, PASI for psoriasis, fecal calprotectin for IBD. That way, you can compare later.
- Monitor closely. Most experts recommend checking in at 4, 8, and 12 weeks after the switch. If you feel off, don’t wait. Call your doctor.
- Track your symptoms. Keep a simple journal: pain levels, energy, sleep, bowel habits. Don’t assume it’s the drug. It might be stress, sleep, or weather.
- Know your rights. In some states, pharmacists can substitute biosimilars automatically if they’re designated "interchangeable." You can refuse. You have a right to the originator if your doctor says so.
The PERFUSE study showed that when patients got a 20-minute counseling session before switching, discontinuation dropped from 18% to just 6.4%. Information reduces fear.
What’s Next?
The first interchangeable adalimumab biosimilar, Cyltezo, was approved by the FDA in 2024. That means pharmacies can swap it for Humira without asking your doctor. It’s a big step toward wider use. But it also means less control for patients.More biosimilars are coming. Over $178 billion in biologic patents expire by 2025. That means more competition, lower prices, and more people getting access. But it also means more switches, more confusion, more anxiety.
The goal isn’t to replace your originator with something "worse." It’s to give you the same outcome at a lower cost. And the evidence shows it works-for most people, most of the time.
It’s not perfect. There are gaps. There are fears. But the science doesn’t lie: if you’re stable, switching to a biosimilar is safe. The bigger risk isn’t the drug-it’s letting fear stop you from getting the care you need.
