The invention relates to novel crystalline forms of (2RS)-1-(4-ethylphenyl)-2-methyl-3-piperidin-1-yl-propan-1-one. The preparation and characterization of the novel crystalline forms according to various embodiments of the invention is described. The invention also relates to pharmaceutical compositions containing the novel crystalline forms, which are useful to treat and/or prevent various conditions such as pathological muscle contracture, myotonic conditions, and spastic paralysis or spasticity caused by various neurologic conditions, and are also useful for the treatment and/or prevention of various types of pain and pathological muscle tension.