Drug therapy is the base of the treatment of psychiatric disorders. Psychotropic drugs can reduce the severity of mental illnesses and improve the outcomes of these disorders if they are used properly. One of the main challenges in psychiatric patients, especially patients who lack enough knowledge about their illness, is the non-compliance with the treatment. In the present study, we first tried to explain the general principles of using psychotropic drugs and then the physicochemical characteristics of each category of psychiatric drugs.