Did a study show prayer made patients worse?

No, and the study's authors did not say so.

The 2006 trial of 1,802 cardiac bypass patients had three groups. Two were told they might or might not be prayed for; one of those received prayer and one did not. A third group was told with certainty that they were being prayed for. In that third group, complications within 30 days occurred in 59 percent of patients, compared with 52 percent in the group that received prayer but was uncertain about it.

The important detail is that both of those groups received exactly the same prayer. The only difference was what patients were told. Whatever produced the difference, it cannot have been the prayer, because the prayer was identical.

Being told before heart surgery that strangers are praying for your survival is a piece of information, and information affects how people feel. The published report gives a relative risk of 1.14 with a 95 percent confidence interval of 1.02 to 1.28, and does not state a p-value for that comparison.

This finding is often reported as evidence that prayer is harmful. That is not what the study showed, and it is worth being careful with, in either direction.