The short answer
Researchers have run randomized trials asking whether being prayed for changes medical outcomes. The largest and best-designed of them found no effect. Research on a person's own faith and spiritual wellbeing is a separate question, and there the findings are real but modest, and they are about coping and quality of life rather than tumors. Prayer is not a treatment, and the evidence does not make it one.
Randomized trials of intercessory prayer have not shown an effect on medical outcomes.
The largest trial, STEP, enrolled 1,802 heart surgery patients and found no benefit.
A Cochrane review of ten trials and 7,646 patients called the findings equivocal.
No trial has tested whether prayer changes cancer survival, tumor response, or recurrence.
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The full explanation.
The claim
Prayer can cure cancer, or measurably improve the odds of surviving it. That goes especially for prayer offered on someone's behalf. The claim shows up in two very different places. One is sincere religious hope. The other is marketing by people selling healing services. This page is about what has been measured. It is not about whether prayer is worth doing.
The plain conclusion
Researchers have tested this. People have been randomly assigned to be prayed for by strangers, without knowing it. Their medical outcomes have not been better than those of people who were not prayed for. And no trial has ever shown that prayer changes cancer survival, tumor response, or recurrence. No trial has measured those things.
What the trials found
The largest study is the Study of the Therapeutic Effects of Intercessory Prayer, published by Benson and colleagues in the American Heart Journal in 2006. It enrolled 1,802 patients having coronary artery bypass surgery at six US hospitals. Prayer was offered for fourteen days, starting the night before surgery. Some patients were told they might or might not receive prayer. Among them, complications within 30 days occurred in 52% of those prayed for and 51% of those not prayed for. The authors' conclusion was that "intercessory prayer itself had no effect on complication-free recovery."
The MANTRA II trial, by Krucoff and colleagues, was published in The Lancet in 2005. It randomized 748 patients undergoing cardiac procedures. It reported that "neither masked prayer nor MIT therapy significantly improved clinical outcome."
A Cochrane systematic review by Roberts and colleagues, updated in 2009, pooled ten trials with 7,646 patients. Its authors wrote that the findings "are equivocal" and that "the evidence does not support a recommendation either in favor or against the use of intercessory prayer." A separate meta-analysis of fourteen studies found an overall effect that "did not differ from zero."
The one odd finding, and what it means
The 2006 trial had a third group. Those patients were told with certainty that they were being prayed for. Complications occurred in 59% of that group, against 52% of the group told they might or might not be. Both groups received exactly the same prayer. The difference was in what patients were told about it.
This is sometimes reported as "prayer made people worse." That is not what the study showed, and the authors did not say it. Being told that strangers are praying for your survival before heart surgery is a piece of information. Information changes how people feel. Whatever produced the difference, it was not the prayer. The prayer was identical in both groups.
What has been studied in cancer
Almost nothing about disease outcomes. There is one substantial cancer trial. Olver and Dutney ran it at the Royal Adelaide Hospital Cancer Centre and published it in 2012. It enrolled 999 patients and measured spiritual wellbeing on a questionnaire. It found a statistically significant improvement, but a very small one: the effect size was reported as a partial eta squared of 0.01. And it was a measure of how people felt, not of how their cancer behaved. Two thirds of participants provided follow-up. It did not look at survival, scans, or recurrence.
The National Cancer Institute has a professional summary on spirituality in cancer care. It discusses coping, spiritual distress, and quality of life at length. It contains no claim that prayer affects cancer survival.
Why the claim persists
An early study from 1988 looked at 393 coronary care patients. It reported that a prayed-for group did better, and it is still cited constantly. Later reviewers pointed out a flaw. It examined a large number of outcomes without specifying in advance which one mattered. That makes a positive result much easier to find by chance. A 1999 replication attempt found a difference on a newly created composite score. But it found no difference in length of stay in intensive care, or in hospital. A widely publicized 2001 study reported that prayer doubled IVF success. It was later removed from the journal's website, and one of its authors was removed from the paper.
There is also a simpler reason. Most people who share these claims are not selling anything. They are frightened, or they love someone who is sick. The claim offers something to do.
The risk worth naming
The danger is not prayer. It is substitution and blame. Delaying a biopsy, stopping a treatment, or declining pain relief because healing is expected can cost a person options they cannot get back. And when the cancer progresses anyway, the patient is left carrying the failure. That is what happens inside a framework where prayer works if you do it properly. The Catechism of the Catholic Church addresses this directly. The line is worth knowing whatever your tradition: "even the most intense prayers do not always obtain the healing of all illnesses."
The bottom line
Trials of prayer as a medical intervention have not found an effect. And none of them studied cancer outcomes. That is a real finding, and it should be stated plainly. It is also a narrow finding. It says nothing about whether prayer is meaningful. It says nothing about whether faith helps a person carry an illness, or what a person owes their own beliefs. Those questions were never on the study forms.
Sources
- https://pubmed.ncbi.nlm.nih.gov/19370557/
- https://pubmed.ncbi.nlm.nih.gov/16569567/
- https://pubmed.ncbi.nlm.nih.gov/16023511/
- https://pubmed.ncbi.nlm.nih.gov/22894887/
- https://pubmed.ncbi.nlm.nih.gov/16827626/
- https://www.cancer.gov/about-cancer/coping/day-to-day/faith-and-spirituality/spirituality-hp-pdq
Words to know
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Common questions
Has anyone actually tested this?
Yes. Several randomized trials assigned patients to be prayed for by strangers, without the patients knowing which group they were in. The largest, published in the American Heart Journal in 2006, enrolled 1,802 cardiac bypass patients. Complications within 30 days occurred in 52% of those prayed for and 51% of those not prayed for.
Was there any effect at all in that trial?
One. Patients who were told with certainty that they were being prayed for had more complications (59%) than patients who were told they might or might not be (52%). Both groups received prayer, so the difference was in what people were told, not in whether prayer happened. The authors did not claim prayer caused harm.
What about cancer specifically?
There is no randomized trial evidence that prayer changes cancer survival, tumor response, or recurrence. A 2012 Australian trial of nearly 1,000 cancer patients measured spiritual wellbeing on a questionnaire, not cancer outcomes, and found a very small improvement.
Does this mean prayer is pointless?
No, and that is not a question a trial can answer. These studies asked a narrow question about measurable medical outcomes. They cannot measure meaning, comfort, community, or what a person's faith is for.
Why does this research keep getting quoted both ways?
A few early small studies reported positive findings and are still widely cited. Larger and better-designed studies that followed did not replicate them, and reviewers have criticized the early studies for testing many outcomes at once and reporting the ones that reached significance.
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Sources last checked: 2026-08-13 what this meansLast updated: 2026-08-13Next planned review: 2027-01-30
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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