"Over the past two decades, a number of studies have shown that Reiki treatments help diminish the negative side effects of chemotherapy, improve surgical outcomes, regulate the autonomic nervous system, and dramatically alter people’s experience of physical and emotional pain associated with illness."
The article links, with the phrase "a number of studies" to what seems to be one study [1]. In this study it looks like they surveyed people who regularly attended reiki practitioners about their trips and found that these people reported positive results.
This doesn't seem like a very compelling study to me. Of course people who go to Reiki will think that it works. That doesn't mean that it does work. People think that placebos work.
I'd like to see a study where half of the Reiki guys are people put through a Reiki training course and the other half are people taught to do the opposite of the intended techniques.
On the one hand, I can see the value of a placebo like institution where people wave their hands and say and do soothing things, and if that makes you feel better, then great. I don't think we need to pretend like this is some kind of mystery though, except as it is a specific case of the more general placebo mystery - which is interesting.
Maybe they go this direction in the article. I stopped reading after it became clear they don't have good evidence that Reiki works.
This also reminds me of the story of an astrologer who genuinely believed in astrology and practiced it according to complicated rules. Somehow he makes a mistake or starts to doubt things, and starts giving people their astrology report (or whatever it would be called) as the opposite of what it should be. Sure enough, the opposite analysis worked just as well as the "correct" analysis.
1 - https://www.ncbi.nlm.nih.gov/pubmed/31638407