A method of mono-therapeutically treating a patient suffering from a condition selected from naïve schizophrenia, therapy resistant schizophrenia, therapy refractory schizophrenia, therapy resistant depression, chronic depression, recurrent depression, and resistant bipolar disorder comprises the administration of a pharmacologically effective amount of a thioxanthene, such as chlorprothixene, flupenthixol, thiotixene, zuclopenthixol, zuclopenthixol acetate and zuclopenthixol decanoate, including a pharmaceutically acceptable salt thereof. Also disclosed is a corresponding use and the manufacture of a corresponding medicament.