Didesmethyl cariprazine-d8 is a deuterium-labeled version of Didesmethyl cariprazine, an orally active metabolite of Cariprazine capable of crossing the blood-brain barrier. It acts as a partial agonist at D2 and D3 receptors and a full agonist at the 5-HT1A receptor, while serving as an antagonist for the human 5-HT2B receptor. Its binding affinities are Ki: 1.41 nM for human D2L, 0.056 nM for human D3, 1.7 nM for human 5-HT1A, and 0.52 nM for human 5-HT2B. Didesmethyl cariprazine also dose-dependently suppresses the spontaneous activity of midbrain dopaminergic neurons in rats.