The story
Probably from me(thyl)s(ulf)o(xy) + (pipe)rid(ine) + (phenothi)azine.
Etymology from Wiktionary, CC BY-SA 4.0.
mesoridazine
Today it means: A phenothiazine tranquilizer C₂₁H₂₆N₂OS₂ used formerly especially in the treatment of schizophrenia and anxiety. Full definition →