The structure of racemic (RS)-trichlorme-thia-zide [systematic name: (RS)-6-chloro-3-(di-chloro-meth-yl)-1,1-dioxo-3,4-di-hydro-2H-1λ6,2,4-benzo-thia-di-azine-7-sulfonamide], C8H8Cl3N3O4S2 (RS-TCMZ), a diuretic drug used in the treatment of oedema and hypertension, was determined from laboratory X-ray powder diffraction data using DASH [David et al. (2006 ▸). J. Appl. Cryst.39, 910-915.], refined by the Rietveld method with TOPAS-Academic [Coelho (2018 ▸). J. Appl. Cryst.51, 210-218], and optimized using DFT-D calculations. The extended structure consists of head-to-tail dimers connected by π-π inter-actions which, in turn, are connected by C-Cl⋯π inter-actions. They form chains propagating along [101], further connected by N-H⋯O hydrogen bonds to produce layers parallel to the ac plane that stack along the b-axis direction, connected by additional N-H⋯O hydrogen bonds. The Hirshfeld surface analysis indicates a major contribution of H⋯O and H⋯Cl inter-actions (32.2 and 21.7%, respectively). Energy framework calculations confirm the major contribution of electrostatic inter-actions (Eelec) to the total energy (Etot). A comparison with the structure of S-TCMZ is also presented.