The enzymes that catalyze the respective steps are as follows: AAA, aryl acylamidase; ASMT, N‐acetylserotonin methyltransferase; COMT, caffeic acid O‐ methyltransferase; AFMK, N1‐acetyl‐N2‐formyl‐5‐methoxykynuramine; IDO, indoleamine 2,3‐dioxygenase; M2H, melatonin 2‐hydroxylase; M3H, melatonin 3‐hydroxylase; 5‐MT, 5‐methoxytryptamine; ROS, reactive oxygen species; RNS, reactive nitrogen species; TDC, tryptophan decarboxylase; TPH, tryptophan hydroxylase; T5H, tryptamine 5‐hydroxylase; SNAT, serotonin N‐acetyltransferase. Dotted lines represent alternative reactions that occur in particular cases.