Clozapine-d8 is the deuterium-labeled analog of the antipsychotic compound Clozapine, wherein eight hydrogen atoms have been replaced with the stable isotope deuterium. Like its parent molecule, Clozapine-d8 acts as a selective ligand for the D4-dopamine receptor and the 5HT2 serotonin receptor, making it a valuable internal standard for the quantitative mass spectrometric analysis of Clozapine, which is an atypical antipsychotic used primarily for the research of treatment-resistant schizophrenia and exhibits high affinity for a diverse number of neuroreceptors beyond its primary targets.