WASHINGTON – Praying for other people to recover from an illness is ineffective, according to the largest, best-designed study to try to examine the power of prayer to heal strangers at a distance.

The study of more than 1,800 heart bypass surgery patients found that those who had other people praying for them had as many complications as those who did not. In fact, one group of patients who knew they were the subject of prayers fared worse.

The long-awaited results, the latest in a series of studies that have failed to find any benefit from “distant” or “intercessory” prayer, came as a blow to the hopes of some that scientific research would validate the popular notion that people can influence the health of people even if they don’t know someone is praying for them.

The researchers cautioned that the study was not designed to test the existence of God or the benefit of other types of prayer, such as praying for oneself or at bedsides of friends or relatives. They also did not rule out that other types of distant prayer may be effective for other types of patients.

“No one single study is ever going to provide an answer,” said Jeffery Dusek of Harvard Medical School, who helped lead the study being published in the April 4 issue of the American Heart Journal.

While many studies have suggested that praying for oneself may reduce stress, research into praying for others who may not even know they are the subject of prayers has been much more controversial. Several studies that claimed to show a benefit have been criticized as deeply flawed. And several of the most recent findings have found no benefit.

The new $2.4 million study, funded primarily by the John Templeton Foundation, was designed to overcome some of those shortcomings. Dusek and his colleagues divided 1,802 bypass patients at six hospitals into three groups. Two groups were uncertain whether they would be the subject of prayers. The third was told they would definitely be prayed for.

The researchers recruited two Catholic groups and one Protestant group to pray “for a successful surgery with a quick, healthy recovery and no complications” for 14 days for each patient, beginning the night before the surgery, using the patient’s first name and the first initial of the last name.

Over the next month, patients in the two groups that were uncertain whether they were the subject of prayers fared virtually the same, with about 52 percent experiencing complications regardless of whether they were the subject of prayers.

Surprisingly, however, 59 percent of the patients who knew they were the targets of prayer experienced complications.

Because the most common complication was an irregular heartbeat, the researchers speculated that knowing they were chosen to receive prayers may have inadvertently put them under increased stress.

“Did the patients think, ‘I am so sick they had to call in the prayer team’?” said Charles Bethea of the Integris Heart Hospital at Baptist Medical Center in Oklahoma City, who helped conduct the study.

Skeptics said the study should put to rest the notion that distant prayer has any effect.

“I would hope that these results, combined with similar recent findings, would encourage scientists to stick to science and stop dabbling in the supernatural,” said Bruce Flamm of the University of California, Irvine.

Even some supporters of incorporating more spirituality in medicine said they hoped the findings would put an end to such research.

“It’s time now to redirect resources toward supporting studies that try to understand how religious faith influences people’s health and well-being through understandable mechanisms,” said Harold Koenig of Duke University.

But proponents of such research said the work was important because so many people believe in prayer.

“I would hate to have premature closure based on a handful of studies,” said Marilyn Schlitz of the Institute of Noetic Sciences in Petaluma, Calif. “We just don’t know enough about this to close the door.”

The findings are unlikely to change the minds of the faithful, several pastors said.

“We welcome and appreciate the involvement of scientists researching faith,” said Rob Brendle, associate pastor of the New Life Church in Colorado Springs, Colo. “But this is just one study. We believe wholeheartedly that prayer changes things. So many of us have experienced that in our lives.”