Abstract: The invention herein disclosed provides a tannin especially effective as antipsychotic drug for mental disorders such as acute and chronic schizophrenia. This tannin composition is represented by the following general formula: ##STR1## wherein l is an integer from 0 to 6, m is 0 or 1, n is an integer from 0 to 6, l+n+m=6;R.sub.1 is hydrogen or G, G representing the galloyl group ##STR2## X is ##STR3## R.sub.2 is OH, . . . OG, or . . . OH; filled dots mean bonding sites, there being no possibility to bond between the mutual fourth positions in each unit; there is only one bonding between the fourth and the sixth position; and there is a total of three galloyl groups in the tannin.