Research into tart cherries and their sleep-promoting properties is still ongoing. The already gathered evidence is compelling and growing steadily.
In a study by Louisiana State University, eight healthy men and women over 50 with chronic insomnia were split between a group which consumed tart cherries and a placebo group. The subjects in the sour cherry group drank approx. 240 ml Montmorency sour cherry concentrate in the morning and evening, the participants in the placebo group received a drink that looked and tasted like sour cherry concentrate.
After two weeks, the sleep behavior was evaluated in questionnaires and this was followed by a two-week phase in which the study participants received neither a placebo nor a cherry juice drink. Then the groups were switched and test subjects who had previously consumed the placebo drink now drank the sour cherry juice for two weeks.
A comparison between the tart cherry and placebo group showed that the tart cherry concentrate extended sleep time by 84 minutes and increased sleep efficiency according to the Pittsburgh sleep quality index, which reflects the subjective perception of sleep quality. 
20 men and women between 18 and 40 years of age and without previously reported sleep disorders took a Montmorency sour cherry drink for seven days. In the study participants who consumed the sour cherries, it was found that the duration of sleep could be increased by an average of 40 minutes. In addition, a comparison with the placebo group showed that tart cherries increased sleep efficiency by 6% and the melatonin level in the blood was increased too. The hormone melatonin is formed in the body from the messenger substance serotonin and is involved in the control of the day-night rhythm. 
In a pilot study of participants who complained of chronic insomnia, the consumption of tart cherries resulted in a significant improvement in the Insomnia Severity Index, one of the most widely used assessment tools in clinical and observational studies on insomnia. The consumption of tart cherries was linked to an improvement in all sleep variables. 
Numerous studies have examined the quality and duration of sleep, as well as the reduction in insomnia associated with the consumption of Montmorency tart cherries. Montmorency tart cherries are one of the few food sources with a high melatonin content. This hormone is responsible for controlling the day-night rhythm in the body and has been shown to improve the quality of sleep. Studies have shown that regular consumption of melatonin-containing tart cherries can improve sleep time and quality, and reduce insomnia.