Escitalopram improves depression by upregulating sphingolipid metabolism; fingolimod (sphingosine-1-phosphate receptor modulator) improves depression; milk sphingomyelin improves gut microbiota balance; phosphatidylcholine (PC) and sphingomyelin (SM) regulate tryptophan metabolism, bile acid metabolism, and vitamin digestion and absorption. Here, S1PR1 is linked to major depressive disorder.