There are several theories as to how prayer might be beneficial during illness, including both scientific and metaphysical explanations.
It has been suggested that patients who pray for themselves or are aware that others are praying for them may develop stronger coping skills and decreased anxiety, thereby potentially improving health outcomes. Other theories include beneficial effects of prayer or "positive thinking" on the immune system, central nervous system (brain), or endocrine (hormonal) system. The meditative, relaxing aspects of prayer have been suggested to have beneficial effects such as lowering blood pressure. There are no plausible scientific explanations for the possible effects of intercessory prayers said without the knowledge of patients.
Metaphysical explanations and beliefs often underlie the practice of prayer. Prayers may be rooted in a belief in the power of a superior being or God who can influence health.
Studies on the effects of intercessory prayer on health outcomes report variable results, with some research finding benefits and other trials noting no effects. Most research in this area is not well designed or reported. There are several difficulties with studies of prayer that make it difficult to form firm conclusions: there are many different types of prayer and religious orientations; intercessors do not always know the identity of patients in studies and therefore prayers are often non-specific; it is challenging to design a study with "placebo" prayer; and there is not widespread agreement on how to best measure outcomes.
These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
There are several studies of intercessory prayer on behalf of patients in intensive care units with severe heart disease or infections. Although some research reports promising results, most trials have not been well designed or reported. As a result, a firm conclusion is not possible.
Limited study of prayer in patients with AIDS reports fewer new AIDS-related illnesses and hospitalizations, although due to methodological problems these results cannot be considered conclusive.
Alcohol or drug dependency:
Initial research reports no effects of intercessory prayer on alcohol or drug dependency. Better research is necessary before a firm conclusion can be drawn.
Prayer has been studied in patients with anxiety but results are mixed.
Blood pressure control:
Initial study reports no effects of intercessory prayer on blood pressure. Better research is necessary before a firm conclusion can be drawn.
Limited research in burn patients reports improved outcomes when prayer is used, although due to methodological problems these results cannot be considered conclusive.
Initial studies in patients with cancer (such as leukemia) report variable effects on disease progression or death rates when intercessory prayer is used. Better quality research is necessary before a firm conclusion can be drawn.
Cardiac bypass (complications):
In one well-designed clinical trial, intercessory prayer had no effect on complication-free recovery from coronary artery bypass surgery. Interestingly, patients that knew they were receiving intercessory prayer (as opposed to those who did not know) were associated with a higher incidence of complications. More study is needed to confirm these results.
There is not enough scientific evidence to make a firm recommendation about prayer for chronic pain.
Prayer appears to be a significant "softening" event for religious couples, facilitating reconciliation and problem-solving based on one study.
Early study suggests psychiatric inpatients might benefit from anonymous distant healing intention.
The potential effect of intercessory prayer on pregnancy rates in women being treated with in vitro fertilization-embryo transfer has been studied. Preliminary results seem positive, but further research is necessary.
Heart disease/heart attack:
Initial studies in patients with heart disease report variable effects on the severity of illness, complications during hospitalization, procedure outcome, or death rates when intercessory prayer is used. Better quality research is necessary before a firm conclusion can be drawn.
Improving health outcomes (general):
There are numerous studies on the effects of intercessory prayer (praying on behalf of patients) on illness severity, death, and well-being of patients or loved ones. Results are variable with some studies reporting benefits of prayer on severity or length of illness and others suggesting no effects. Most research has not been well designed or reported and as a result, a firm conclusion is not possible. Additional research is needed in this area with clear descriptions of prayer techniques and well-defined health outcomes.
Several studies in which patients knew that prayers were being said on their behalf report benefits, although it is not clear that prayer is superior to other forms of compassionate interaction.
Prayer may help reduce the length of hospital stay as well as the duration of fever in patients with infections. However, early study is controversial and additional study is needed before a conclusion can be drawn.
Kidney disease (kidney transplant):
Preliminary research shows positive trends associated with prayer and spirituality in patients with end stage renal disease who are coping after kidney transplant. Further research is needed before conclusions can be drawn.
Initial studies report fewer birth complications in people who are religious or pray, although due to methodological problems, these results cannot be considered conclusive.
Preliminary study suggests that older adults who participate in private religious activity before the onset of impairment in activities of daily living appear to have a survival advantage over those who do not. Further research is needed to confirm these results.
Forty-eight percent of the homeless women in one study reported that the use of prayer significantly related to less use of alcohol and/or street drugs, fewer perceived worries, and fewer depressive symptoms. Further research is needed before a firm conclusion can be drawn in this area.
Quality of life in chronically ill patients:
Limited study reports improved quality of life in patients who desire others to pray for them and receive healing. Better quality research is necessary before a firm conclusion can be drawn.
Initial research suggests that in-person intercessory prayer (praying by others in the presence of patients) may reduce pain, fatigue, tenderness, swelling, and weakness when it is used in addition to standard care. Better quality research is necessary before a firm conclusion can be drawn.
Sickle cell anemia:
Prayer has been studied as a coping mechanism for patients with sickle cell disease with mixed results.
There is some research that suggests that religiously active persons may be less likely to smoke cigarettes or, if they do smoke, may be likely to smoke fewer cigarettes.
Prayer has not been shown to help prevent or treat diabetes or related health issues. Diabetes should be treated by a qualified healthcare professional using proven therapies.
Early study suggests that distant healing by experienced healers may have no effect in removal or size of skin warts.