The vast majority of reports on the effectiveness of Reiki appear in popular rather than scientific literature. Proponents of Reiki cite the growing body of research in the field of Therapeutic Touch as evidence of the therapeutic transfer of energy through touch.

One California study showed that Reiki can increase hemoglobin and hematocrit levels. The study compared 47 people participating in Reiki training and a small control group of 9 healthy medical professionals. The study found a significant increase in hemoglobin and hematocrit levels among the Reiki group and no significant change in the control group.