(2Z)-2-[Cyano(2,3-dichlorophenyl)methylene]hydrazinecarboximidamide-13C3D3 is the isotope labeled form of (2Z)-2-[Cyano(2,3-dichlorophenyl)methylene]hydrazinecarboximidamide (C979120), which has been identified as an impurity of Lamotrigine (L173250).