Geissoschizine methyl ether, a major indole alkaloid found in Uncaria hook, is a major active component of Yokukansan with psychotropic effects. Geissoschizine methyl ether is potent 5-HT1A receptor agonist[1][2].
[1]. Matsumoto T, et al. In vitro identification of human cytochrome P450 isoforms involved in the metabolism of Geissoschizine methyl ether, an active component of the traditional Japanese medicine Yokukansan. Xenobiotica. 2016;46(4):325-34. [2]. Nishi A, et al. Geissoschizine methyl ether, an alkaloid in Uncaria hook, is a potent serotonin ?A receptor agonist and candidate for amelioration of aggressiveness and sociality by yokukansan. Neuroscience. 2012 Apr 5;207:124-36.