N’-[2-[2,4-Dimethylphenyl)thio]phenyl] Vortioxetine-d8 is labelled N’-[2-[2,4-Dimethylphenyl)thio]phenyl] Vortioxetine (D477790), an impurity of Vortioxetine (V766000, HBr salt) which is a multimodal serotonergic agent, inhibits 5-HT1A, 5-HT1B, 5-HT3A, 5-HT7 receptor and SERT.