Desmethyl cariprazine-d8 is the deuterium labeled Desmethyl cariprazine (HY-100656). Desmethyl cariprazine is a major active metabolite of cariprazine, with activities at human dopamine receptors and serotonin receptors, showing a pEC50 of 8.90 at human D2 receptors, a pEC50 of 8.09 at D3 receptors, and a pEC50 of 6.28 at 5-HT1A receptors. Desmethyl cariprazine inhibits forskolin-induced cAMP production at D2, D3 and 5-HT1A receptors, and suppresses serotonin-induced Ca2+ release at 5-HT2B receptors. Desmethyl cariprazine is applicable to research related to schizophrenia, bipolar disorder type I and bipolar disorder.