If you’ve ever prayed for someone who is sick, you may actually be doing him or her harm.

Strangers’ prayers for heart-surgery patients may have had detrimental effects on those patients, according to a study conducted by a team of Harvard Medical School (HMS) researchers in conjunction with other medical experts.

The study, which began almost ten years ago and was released in April’s American Heart Journal, divided 1,802 bypass surgery patients into three groups.

Two groups were prayed for: one group of patients was informed they were being prayed for, and the other group was not informed either way. The third group’s members did not have strangers pray for them and were also not informed either way.

The strangers making the prayers were given a patient’s first name and last initial and were told to pray for a quick recovery with no complications.

Fifty-nine percent of the people who knew they were being prayed for had complications after surgery, while 52 percent of the people who did not know whether they were being prayed for experienced complications.

Reverend Dean Marek of the Mayo Clinic, a researcher who worked on the study, said in a press release that he didn’t anticipate these results.

“Obviously, my research colleagues were surprised by the unexpected and counterintuitive outcome,” he said.

Knowing that they were being prayed for may have caused patients to experience “performance anxiety,” meaning that they thought they were being prayed for because their prognosis was grim, the researchers speculated.

The study cost $2.4 million. It was funded by the John Templeton Foundation, which seeks to study the intersection between religion and science.

Although previous studies had been conducted on the effects of prayer, limitations such as small sample sizes affected their accuracies, according to HMS researcher Jeffrey Dusek.

About 43 percent of American adults have prayed for their own health, and 25 percent have had others pray for them, according to a 2004 survey conducted by the National Center for Health Statistics.

Terri Cisse, a graduate student at the Harvard Divinity School, questioned the validity of the study.

“I’ve seen firsthand from working at the Dana-Farber Cancer Institute how people are consoled by prayer. Prayer is so transcendent and metaphysical that it can’t be measured scientifically,” she said. “There are different rubrics for evaluating science and religion.”

Critics of the study, including Dr. Mitchell Krucoff of Duke University, published an editorial in the American Heart Journal claiming that researchers took “an almost casual approach toward any explanation.”

Dusek said that the scientists’ experiment was worthwhile, despite the lack of definitive results.

“We were scientifically valid in trying...to ask a question that has never been asked before.”

However, another critic, Dr. Harold Koenig, founder of Duke’s Center for the Study of Religion/Spirituality, said the study overlooked the importance of sincerity of prayers.

“God isn’t like a Coke machine, where you put in 50 cents and get one size and put in one dollar and get another size,” he said, adding that the study was a waste of money.