The body of research around Reiki and other energy healing methods is growing all the time. Most of the links below are to the PubMed site, which is maintained by the US National Library of Medicine and National Institutes of Health. Some of the PubMed pages have links to the full-text article; I would encourage you to read not just the abstract, but the entire article if it’s available.
A systematic review is a critical examination of available peer-reviewed research on a particular subject. From a scientific perspective, a systematic review is considered the highest level of evidence: Morero JAP, Pereira SS, Esteves RB, Cardoso L. Effects of Reiki on Mental Health Care: A Systematic Review. Holist Nurs Pract. 2021 Jul-Aug 01;35(4):191-198. doi: 10.1097/HNP.0000000000000456. PMID: 34115737.
Bondi A, Morgan T, Fowler SB. Effects of Reiki on Pain and Anxiety in Women Hospitalized for Obstetrical- and Gynecological-Related Conditions [published online ahead of print, 2020 Jul 3]. J Holist Nurs. 2020;898010120936437. doi:10.1177/0898010120936437
The Davis article looks at Healing Touch, a close cousin of Reiki:
Gantt, M., & Orina, J. A. T. (2019). Educate, Try, and Share: A Feasibility Study to Assess the Acceptance and Use of Reiki as an Adjunct Therapy for Chronic Pain in Military Health Care Facilities. Military Medicine. doi:10.1093/milmed/usz271
Dyer, N. L., Baldwin, A. L., & Rand, W. L. (2019). A Large-Scale Effectiveness Trial of Reiki for Physical and Psychological Health. Journal of Alternative and Complementary Medicine, 25(12), 1156-1162. doi:10.1089/acm.2019.0022
Zucchetti, G., Candela, F., Bottigelli, C., Campione, G., Parrinello, A., Piu, P., . . . Fagioli, F. (2019). The Power of Reiki: Feasibility and Efficacy of Reducing Pain in Children With Cancer Undergoing Hematopoietic Stem Cell Transplantation. Journal of Pediatric Oncology Nursing, 36(5), 361-368. doi:10.1177/1043454219845879
Zins, S., Hooke, M. C., & Gross, C. R. (2019). Reiki for Pain During Hemodialysis: A Feasibility and Instrument Evaluation Study. Journal of Holistic Nursing, 37(2), 148-162. doi:10.1177/0898010118797195
Vergo, M. T., Pinkson, B. M., Broglio, K., Li, Z., & Tosteson, T. D. (2018). Immediate Symptom Relief After a First Session of Massage Therapy or Reiki in Hospitalized Patients: A 5-Year Clinical Experience from a Rural Academic Medical Center. Journal of Alternative and Complementary Medicine, 24(8), 801-808. doi:10.1089/acm.2017.0409
Jahantiqh, F., Abdollahimohammad, A., Firouzkouhi, M., & Ebrahiminejad, V. (2018). Effects of Reiki Versus Physiotherapy on Relieving Lower Back Pain and Improving Activities Daily Living of Patients With Intervertebral Disc Hernia. J Evid Based Integr Med, 23, 2515690×18762745. doi:10.1177/2515690×18762745
Radziewicz, R. M., Wright-Esber, S., Zupancic, J., Gargiulo, D., & Woodall, P. (2018). Safety of Reiki Therapy for Newborns at Risk for Neonatal Abstinence Syndrome. Holistic Nursing Practice, 32(2), 63-70. doi:10.1097/hnp.0000000000000251
McManus, D. E. (2017). Reiki Is Better Than Placebo and Has Broad Potential as a Complementary Health Therapy. Journal of Evidence-Based Complementary & Alternative Medicine, 22(4), 1051-1057. doi:10.1177/2156587217728644
Mangione, L., Swengros, D., & Anderson, J. G. (2017). Mental Health Wellness and Biofield Therapies: An Integrative Review. Issues in Mental Health Nursing, 38(11), 930-944. doi:10.1080/01612840.2017.1364808
Baldwin, A. L., Vitale, A., Brownell, E., Kryak, E., & Rand, W. (2017). Effects of Reiki on Pain, Anxiety, and Blood Pressure in Patients Undergoing Knee Replacement: A Pilot Study. Holistic Nursing Practice, 31(2), 80-89. doi:10.1097/hnp.0000000000000195
Thrane, S. E., Maurer, S. H., Ren, D., Danford, C. A., & Cohen, S. M. (2017). Reiki Therapy for Symptom Management in Children Receiving Palliative Care: A Pilot Study. American Journal of Hospice and Palliative Care, 34(4), 373-379. doi:10.1177/1049909116630973
Sagkal Midilli, T., & Ciray Gunduzoglu, N. (2016). Effects of Reiki on Pain and Vital Signs When Applied to the Incision Area of the Body After Cesarean Section Surgery: A Single-Blinded, Randomized, Double-Controlled Study. Holistic Nursing Practice, 30(6), 368-378. doi:10.1097/hnp.0000000000000172
Kirshbaum, M. N., Stead, M., & Bartys, S. (2016). An exploratory study of reiki experiences in women who have cancer. International Journal of Palliative Nursing, 22(4), 166-172. doi:10.12968/ijpn.2016.22.4.166
Thrane S, Cohen SM. Effect of Reiki therapy on pain and anxiety in adults: an in-depth literature review of randomized trials with effect size calculations. Pain Manag Nurs. 2014;15(4):897-908. doi:10.1016/j.pmn.2013.07.008
Díaz-Rodríguez L, Arroyo-Morales M, Fernández-de-las-Peñas C, García-Lafuente F, García-Royo C, Tomás-Rojas I. Immediate effects of reiki on heart rate variability, cortisol levels, and body temperature in health care professionals with burnout. Biol Res Nurs. 2011;13(4):376-382.
In the interest of scientific honesty, negative or neutral results are still results:
Catlin A, Taylor-Ford RL. Investigation of standard care versus sham Reiki placebo versus actual Reiki therapy to enhance comfort and well-being in a chemotherapy infusion center. Oncol Nurs Forum. 2011;38(3):E212-E220. doi:10.1188/11.ONF.E212-E220
Dr. Bill Bengston and his colleagues have conducted rigorous experiments using his energy healing method and have see statistically significant results in slowing, and in some cases reversing, tumor growth in a mouse model. He has also experimentally demonstrated that healing can be stored in live subjects and everyday objects, and even recorded. His website is a fascinating read.
Beseme S, Fast L, Bengston W, Turner M, Radin D, McMichael J. Effects Induced In Vivo by Exposure to Magnetic Signals Derived From a Healing Technique. Dose Response. 2020;18(1):1559325820907741. Published 2020 Mar 30. doi:10.1177/1559325820907741
Beseme S, Bengston W, Radin D, Turner M, McMichael J. Transcriptional Changes in Cancer Cells Induced by Exposure to a Healing Method. Dose Response. 2018;16(3):1559325818782843. Published 2018 Jul 11. doi:10.1177/1559325818782843
The Center for Reiki Research includes a section on Reiki in hospitals. This site requires you to sign up for a free membership.