Background: Prayer is an ancient and widely used intervention for alleviating illness and promoting good health. Whilst the outcomes of trials of prayer cannot be interpreted as 'proof/disproof' of God's response to those praying, there may be an effect of prayer not dependent on divine intervention. This may be quantifiable; which makes this investigation of a widely used health care intervention both possible and important.
Objectives: To review the effectiveness of intercessory prayer as an additional intervention for those with health problems already receiving standard medical care.
Search strategy: We systematically searched ten databases (June 2005).
Selection criteria: We included any randomised trial of personal, focused, committed and organised intercessory prayer with those interceding holding some belief that they are praying to a God. This prayer should be offered on behalf of anyone with health problems.
Data collection and analysis: We extracted data independently and analysed on an intention to treat basis calculating, for binary data, the fixed effect relative risk (RR), their 95% confidence intervals (CI), and the number needed to treat or harm (NNT or NNH).
Main results: Ten studies are now included (n=7646). We found a slight difference between groups, favouring prayer for death (6 RCTs, N=6782, RR 0.88 CI 0.80 to 0.97, NNT 42 CI 25 to 167, I(2 )83%) but no differences between groups for clinical state, complications or leaving the study early. Individual studies did find some effects. One trial separated death data into 'high' and 'low' risk and found prayer had a positive effect on those at 'high' risk of death (1 RCT, N=445, RR 0.3 CI 0.2 to 0.46, NNT 8 CI 7 to 11). A second study found a positive effect of prayer on women undergoing IVF treatment with significantly more successful implantations in the prayer group compared with standard care (1 RCT, n=169, RR 0.68 CI 0.53 to 0.86, NNT 5 CI 3 to 10). A larger study assessed the effect of awareness of prayer and found those aware of receiving prayer had significantly more post operative complications than those not receiving prayer (1 RCT, n=1198, RR 1.15 CI 1.04 to 1.28, NNH 14 CI 8 to 50) and those uncertain if they were receiving prayer (1 RCT, n=1205, RR 1.12 CI 1.01 to 1.24, NNH 17 CI 9 to 201)
Authors' conclusions: It is not sensible to interpret any of the interesting results with great confidence. However, for women hoping for successful IVF treatment there are some data suggesting a favourable outcome of prayer but these data are derived from only one of the smaller trials. On the other hand, one of the larger studies suggests that those undergoing operations may not wish to know of the prayer that is being offered on their behalf. Most data are equivocal. The evidence presented so far is interesting enough to justify further study into the human aspects of the effects of prayer. However it is impossible to prove or disprove in trials any supposed benefit that derives from God's response to prayer.