Over the years the National Institutes of Health (NIH) and the National Center for Complementary and Integrative Health (NCCIH) has completed five studies looking at Reiki's ability to benefit people. Overlapping data from some of the stronger studies support the ability of Reiki to reduce anxiety and pain, and suggest its usefulness to induce relaxation, improve fatigue and depressive symptoms, and strengthen overall well being.

Unlike antidepressants, which claim that effects and restoration of serotonin and norepinephrine levels may take years before improvements are noticed, most Reiki patients claim that they leave the Reiki session feeling relaxed and rejuvenated.

Studies such as the Shore experiment and Meland case studies (https://healthpsych.psy.vanderbilt.edu/2009/Reiki.htm) provide evidence that Reiki healing does aid in the lessening of stress and reducing the symptoms of physical pain and mental illness. Although the mechanism of how Reiki targets the mind and the body is yet unclear, there is evidence that Reiki treatments reduce symptoms of depression, as well as other physically related illnesses.

Relaxation achieved through Reiki often reduces cortisol levels in the blood, resulting in body restoration to improved health levels allowing the patient to become better equipped to handle stress and lessen feelings of anxiety.