The invention relates to particular substituted deuterated heterocycle fused gamma-carbolines, their prodrugs, in free, solid, pharmaceutically acceptable salt and/or substantially pure form as described herein, pharmaceutical compositions thereof, and methods of use in the treatment of diseases involving 5-HT2A receptor, serotonin transporter (SERT) and/or pathways involving dopamine D1/D2 receptor signaling systems, and/or the treatment of residual symptoms.