For this study, researchers wanted to investigate the connections between IBD, supplementing melatonin, and the subsequent immune responses and bacterial compositions in the guts of mice. To do so, they created a mouse model of IBD, administering melatonin to a portion of them.

Based on their analysis, melatonin actually made symptoms and recovery worse for the mice who had been administered melatonin, showing worsened gut inflammation, and during remission, slower recovery.

Namely, the mice who’d been administered melatonin showed notable signs of colitis aggravation, delayed recovery, and increased inflammatory markers, which the study authors say confirm the harmful effects of melatonin supplementation on a disrupted gut barrier.

While these findings have yet to be replicated in humans, study co-author and immunologist Cristina Ribeiro de Barros Cardoso Ph.D. notes that people should be scrutinous when it comes to hormonal supplements.

“Our study shows that people should be careful about taking hormone supplements and that the ingestion of melatonin as a supplement can have adverse effects on health,” she says in a news release, adding, “[Melatonin is] a hormone and regulation of the interaction between all hormones and the immune system is very delicate.”