1,3,4,6,7,11b-Hexahydro-1-isobutyl-9,10-dimethoxy-2H-benzo[a]quinolizin-2-one-d7 is the isotope labelled analog of 1,3,4,6,7,11b-Hexahydro-1-isobutyl-9,10-dimethoxy-2H-benzo[a]quinolizin-2-one (H294395); an impurity of Tetrabenazine (T284000) which is a dopamine depleting agent, an antidyskinetic and antipsychotic.