Biosimilar Switching: What Happens When You Change From Originator

When you’ve been taking a biologic drug for years - maybe for rheumatoid arthritis, Crohn’s disease, or psoriasis - your body knows it. Your symptoms are under control. You’ve figured out the injection routine. You know how you feel on it. Then your doctor says: we’re switching you to a biosimilar. It’s cheaper. Your insurance requires it. Maybe you’ve never even heard the word before. What happens now?

Biosimilars aren’t generics. 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 - proteins, antibodies, enzymes. Think of it like trying to recreate a handmade ceramic vase. You can get very close. You can match the shape, the glaze, the weight. But no two are ever perfectly identical. That’s why regulators don’t call them "identical" - they call them "highly similar." And that’s where the confusion starts.

How Do You Even Know a Biosimilar Works the Same?

Before a biosimilar gets approved, it goes through more than 250 lab tests comparing it to the original drug. These aren’t simple checks. They look at the protein’s 3D structure, how it binds to targets, how fast it breaks down in the body, even tiny differences in sugar molecules attached to it. Then it’s tested in healthy volunteers to see if it moves through the bloodstream the same way. Finally, it’s tested in patients with the same condition - comparing how well it controls inflammation, how often side effects happen, and whether the immune system reacts to it.

Over 100 clinical studies have been done since the first biosimilar was approved in Europe in 2006. The results? No clinically meaningful difference in safety or effectiveness. That’s not just a phrase. It’s a regulatory standard. In the NOR-Switch study, 481 patients switched from originator infliximab to its biosimilar CT-P13. After a year, 53% were still on the biosimilar. The original drug group? 60%. The difference wasn’t statistically significant. People weren’t getting sicker. Their bloodwork looked the same. Their disease scores didn’t change.

What Actually Happens When You Switch?

For most people, nothing noticeable. You get your next injection. The needle feels the same. The pen clicks the same. The pharmacy gives you a different box. You go about your day. And your symptoms? Still controlled. Studies show over 85% of patients stay on the biosimilar after 12 months. That’s true across conditions - rheumatoid arthritis, psoriatic arthritis, inflammatory bowel disease. Even when switching from one biosimilar to another - say, from CT-P13 to SB2 - the retention rate stays above 90% in stable patients.

Take a real example: a 48-year-old woman with Crohn’s disease on infliximab for five years. Her fecal calprotectin - a marker of gut inflammation - was at 124 μg/g. After switching to the biosimilar SB2, it dropped to 118 μg/g. No flare. No new symptoms. Her doctor didn’t change anything else. She didn’t even notice.

But here’s the catch: not everyone feels the same.

Why Do Some People Stop Taking It?

It’s not always about the drug. It’s about the mind.

A 2021 study in Frontiers in Psychology found that 32.7% of patients reported new or worse symptoms after being switched - even when lab tests showed no change. They felt different. They thought the medicine wasn’t working. They blamed the switch. This is called the nocebo effect - the opposite of placebo. If you expect something to go wrong, your body can make it happen.

Online forums are full of stories. Reddit threads titled "Why do I feel worse after my biosimilar switch?" People describe fatigue, joint pain, rashes. But when doctors check their blood, their drug levels, their inflammation markers - everything’s normal. The problem isn’t the biosimilar. It’s the fear of change.

Then there are the real side effects. Some people develop injection-site reactions. Others report headaches or dizziness. In one psoriasis study, 14.3% of patients on a biosimilar had skin reactions compared to 10.7% on the originator. That’s a small but real difference. But here’s the key: these reactions were mild. They didn’t lead to hospitalization. And in most cases, they went away with time or a simple change in injection technique.

True immunogenicity - the body making antibodies that neutralize the drug - is rare. Studies show only about 1.7 events per 100 patient-years. That’s less than 2% of people over a year. And even then, it doesn’t always mean the drug stops working. Many patients can be managed with dose adjustments.

Who Shouldn’t Switch?

Not everyone is a good candidate. If your disease is active - if your joints are swollen, your bowels are inflamed, your skin is flaring - switching is risky. Stability is key. Experts recommend switching only when your disease is well-controlled for at least 3-6 months. If you’ve had a recent flare, or if you’re on a high dose, stay on what you know.

Also, if you’ve already switched once - from originator to biosimilar - and you’re doing well, don’t switch again unless your doctor says so. Switching multiple times increases the chance of immune reactions. One study found a 15.3% discontinuation rate after a second switch in IBD patients. That’s higher than the first switch. The body can get confused.

And if you’re pregnant, planning pregnancy, or breastfeeding? Talk to your doctor. There’s less data here. Most biosimilars are considered safe based on their originator, but individual decisions matter.

Cost and Access: The Real Reason for Switching

Biosimilars cost 15% to 35% less than the original drug. In the U.S., when Humira’s first biosimilars launched in 2023, they hit the market at a 35% discount. That’s billions in savings for insurers and patients. In Europe, 67% of filgrastim prescriptions are now biosimilars. In the U.S., it’s only 24% - because of complex rebate deals between drugmakers and pharmacy benefit managers. But that’s changing. By 2023, 85% of U.S. health plans had mandatory switch policies for certain biologics.

That means if you’re on adalimumab or infliximab, you’re likely to be switched. Not because your doctor wants to - but because your insurance requires it. That’s the reality. And it’s not going away. Over $178 billion in biologic patents are expiring through 2025. More biosimilars are coming. More switches are coming.

What You Can Do Before and After the Switch

You don’t have to be passive in this process.

Before the switch: Ask your doctor for a 20-minute conversation. Don’t just sign a form. Ask: "What are the risks? What will we monitor? What if I feel worse?" Get a copy of your latest lab results - drug trough levels, inflammation markers. Keep them. You’ll need them later.

After the switch: Track how you feel for the first three months. Keep a simple journal: energy levels, joint pain, bowel habits, skin condition. Note any new symptoms. Don’t assume it’s the drug. Stress, sleep, diet, infections - they all play a role. But if something feels off, tell your doctor. Don’t wait.

Some clinics now use shared decision-making tools - simple charts that show you the evidence: "9 out of 10 people do fine after switching." Seeing that data helps reduce fear.

And if you’re switched without warning? You still have rights. Ask for a delay. Ask for a trial period. Many doctors will agree if you’re stable and concerned.

The Bottom Line

Switching from an originator biologic to a biosimilar is safe for most people with stable disease. The science is clear. The data is strong. The cost savings are real. You’re not getting a lesser drug. You’re getting a drug that works just as well - for a fraction of the price.

But safety isn’t just about blood tests. It’s about trust. It’s about how you feel. If you’re anxious, your fear can make you sick. That’s why communication matters more than ever. Your doctor should explain why the switch is happening. You should know what to watch for. And you should feel heard.

Most people adapt without issue. Their lives don’t change. Their symptoms stay gone. Their wallets get a little lighter. And the system saves money - money that can be used to help others get treatment too.

It’s not perfect. There are exceptions. There are people who do worse. But those cases are rare - and often not because of the drug. They’re because of fear, lack of support, or poor timing.

If you’re being switched, ask questions. Track your symptoms. Give it time. And remember: you’re not being experimented on. You’re being offered a proven, safe, and affordable alternative - backed by over a decade of global evidence.