While there have been some published papers regarding the Solfeggio Frequencies, there is still much research to be done. New research is on the way! Here are some papers that studied the Solfeggio Frequencies.
A 2018 study on 528hz frequencies and how the effect the endocrine system by Kaho Akimoto, Ailing Hu, and Takuji Yamaguchi showed that a group of people who listened to 528hz tones had decreased stress compared to a control group.
A paper done on the Effects of 528 Hz Sound Wave to Reduce Cell Death in Human Astrocyte Primary Cell Culture Treated with Ethanol found the use of these sound waves can be useful to reduce the toxic effects of ethanol on astrocytes cells culture.
Lili Naghdi, Heidi Ahonen, Pasqualino Macario, and Lee Bartel have a clinical study showing the effect of low-frequency sound stimulation on patients with fibromyalgia.