Confirmation Bias in Medicine: How It Skews Treatment Decisions

When you believe a drug works because it worked for a friend, or dismiss a generic because it looks different, you’re not being irrational—you’re falling into confirmation bias, a mental shortcut where people favor information that confirms their existing beliefs while ignoring contradictory evidence. Also known as positive bias, it’s not just a flaw in thinking—it’s a quiet killer in healthcare. This isn’t about being stupid. It’s about how our brains are wired to save energy. If you’ve had a bad experience with a brand-name drug, you might assume all generics are inferior—even when they’re chemically identical. That’s confirmation bias at work.

Doctors aren’t immune. A physician who believes SSRIs cause weight gain might overlook studies showing sertraline has minimal impact, while fixating on paroxetine cases that fit their belief. In the clinic, this means patients get the wrong drug—not because it’s unsafe, but because the doctor didn’t look hard enough for data that contradicted their assumption. And it’s not just about medications. When patients refuse glaucoma surgery because they heard someone lost vision after the procedure, they’re filtering reality through fear, not facts. The same thing happens with nocebo effect, when negative expectations cause real physical symptoms. It’s the flip side of confirmation bias: if you expect side effects from a generic, your body often delivers them—even if the pill is identical to the brand. Even authorized generics, brand-name drugs sold under a generic label at lower prices. It’s the same medicine, same factory, same quality—but patients still report worse results just because the label changed. This isn’t science. It’s psychology. And it’s costing people better care.

Look at the posts below. You’ll see how confirmation bias shows up in every corner of medicine: in the fear of switching from brand to generic, in the dismissal of new treatments like MIGS for glaucoma because "old surgery worked fine," in the belief that diphenhydramine is safe for sleep just because it’s over-the-counter. You’ll see how patients and providers alike ignore data that contradicts their gut feeling. These aren’t isolated cases. They’re patterns. And they’re preventable—if you know what to look for.