In 2003, a team of researchers from several American universities launched a small clinical trial, the results of which should not have been a surprise. Of the patients taking the active drug, an anticonvulsant intended to reduce epileptic seizures, 86 percent saw their seizure frequency fall. So did 79 percent of the patients that received a sham treatment, or a placebo.
It seemed like a classic example of the placebo effect, with one notable difference: The patients were dogs.
“As I did these placebo-controlled studies and I was evaluating data, I was like, ‘Oh, look, these dogs are getting better on the placebo,’” says Karen Munana, a veterinary neurologist at North Carolina State University who co-authored the study. That response had never been reported for epilepsy treatments in dogs before, she says.
At the time, double-blind placebo-controlled trials—the gold standard for evaluating new medical treatments—were relatively uncommon in veterinary medicine. But if Munana and her colleagues hadn’t done one, they would have misjudged how well the drug, levetiracetam, worked. “If I had not had the placebo arm [of the study], I would’ve said that this drug was effective,” she says.
While the placebo effect is a well-established phenomenon in human patients, it’s an underappreciated one in veterinary medicine. And the particular way it plays out in veterinary care highlights how unconscious cognitive biases can mislead humans when we care for other species. Even when pet owners are determined to provide first-rate care for the animals they love, these blind spots can undermine their best efforts. “The stories that we tell about our pets often aren’t really reflecting what’s happening to their bodies,” says Brennen McKenzie, a veterinarian and the author of SkeptVet, a blog dedicated to evidence-based veterinary medicine.