Intercessory prayer is prayer which is undertaken on behalf of others. The intercessor uses prayer to communicate with ‘God’, making a request on behalf of someone else or on behalf of a group of people.
Anecdotes (hear say) abound within religious circles about how certain people have been healed miraculously as a result of people praying for them. Since they are anecdotes, most people in the medical community generally remain sceptical of such claims.
A number of attempts have been made to evaluate the success rate of prayer in controlled conditions. Ideally, if praying for someone actually works, it ought to be demonstrable in a way that can be independently corroborated without being influenced by the bias of the person reporting the miracle.
To this end, a number of scientific studies have been conducted to test the efficacy of intercessory prayer.
Here are examples of such studies (click the links to read the abstracts of those studies):
Study of the Therapeutic Effects of Intercessory Prayer (STEP) in cardiac bypass patients: a multicenter randomized trial of uncertainty and certainty of receiving intercessory prayer (considered to be by far the most comprehensive and rigorous investigation of third-party prayer to date)
NO, it does not work.