According to a Study published in The December 2019 issue of the Journal of Alternative and Complementary Medicine, the authors evaluated  the effectiveness of a single session of Reiki on physical and psychological health in a large sample.  The result of the study was that statistically significant improvements were observed for all outcome measures, including pain, drowsiness, tiredness, nausea, appetite, shortness of breath, anxiety, depression, and overall well-being. The study can be accessed at https://pubmed.ncbi.nlm.nih.gov/31638407/