It was one of those findings that would change medicine, Dr. Christopher Lewandowski thought.

For years, doctors had tried — and failed — to find a treatment that would preserve the brains of stroke patients. The task was beginning to seem hopeless: Once a clot blocked a blood vessel supplying the brain, its cells quickly began to die. Patients and their families could only pray that the damage would not be too extensive.

But then a large federal clinical trial proved that a so-called clot-buster drug, tissue plasminogen activator (T.P.A.), could prevent brain injury after a stroke by opening up the blocked vessel. Dr. Lewandowski, an emergency medicine physician at Henry Ford Health System in Detroit and the trial’s principal investigator, was ecstatic.

“We felt the data was so strong we didn’t have to explain it” in the published report, he said.

He was wrong. That groundbreaking clinical trial concluded 22 years ago, yet Dr. Lewandowski and others are still trying to explain the data to a powerful contingent of doubters.

The skeptics teach medical students that T.P.A.is dangerous, causing brain hemorrhages, and that the studies that found a benefit were deeply flawed. Better to just let a stroke run its course, they say.