Co-crystallization of racemic 1-cyclo­hexyl-1-phenyl-3-(piperidin-1-yl)propan-1-ol (trihexyphenid­yl) with 3,5-di­nitro­benzoic acid gives a simple 1:1 salt, namely 1-(3-cyclo­hexyl-3-hy­droxy-3-phenyl­prop­yl)piperidin-1-ium 3,5-di­nitro­benzoate, C₂₀H ₃₂NO ⁺·C ₇H ₃N ₂O ₆ ⁻, (I), whereas a similar co-crystallization using (Z)-3-(2-chloro-9 H-thioxanthen-9-yl)- N, N-di­methyl­propan-1-amine (chlorprothixene) gives a 1:2 acid salt, namely (Z)-3-(2-chloro-9 H-thioxanthen-9-yl)- N, N-di­methyl­propan-1-aminium hydrogen bis­(3,5-di­nitro­benzoate), C₁₈H ₁₉ClNS ⁺·[H(C ₇H ₃N ₂O ₆) ₂] ⁻, (II), the anion of which contains a very short O—H⋯O hydrogen bond, with dimensions O—H = 1.04 (3) Å, H⋯O = 1.41 (3) Å, O⋯O = 2.4197 (15) Å and O—H⋯O = 161 (3)°. In the cation of (I), the cyclo­hexyl and piperidyl rings both adopt chair conformations, whereas in the cation of (II), the central heterocyclic ring adopts a boat conformation, so that the dihedral angle between the two aryl rings is 41.56 (4)°. A combination of O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds links the ions of (I) into a complex chain of rings, and these chains are linked into sheets by π– π stacking inter­actions between inversion-related pairs of anions. In compound (II), a different combination of O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds links the ions into sheets. Comparisons are made with some related structures.