In this study, the binary and the ternary phase diagrams of R-/S-ketamine were determined based on differential scanning calorimetry (DSC) measurements. The binary phase diagram presented a eutectic point in the 50:50 (R/S) composition which characterizes the product as a conglomerate forming system. On the other hand, the ternary phase diagram in the presence of ethanol showed a eutectic point in the 75:25 (R/S) composition, indicating the occurrence of a racemic compound. The observed facts indicate that the solvent and the temperature may affect the eutectic point, and thus different crystal forming systems can be obtained from the melt and from the solution. The calorimetric method was demonstrated to be an excellent short-cut method for the fast construction of phase diagrams, taking only some hours and consuming only a few milligrams [(5 to 20) mg] of samples.