Phencyclidine organic mental disorder is a mental impairment believed to result from chronic phencyclidine use. It is characterized by memory deficits and a state of confusion or decreased intellectual functioning with associated assaultiveness. Visual disturbances and speech difficulty, such as blocking (inability to retrieve the proper words), also occur. A differential diagnosis should rule out other possible causes of organicity. The course of the disorder may be quite variable. The reasons for this variability are not clear but may be related to residual drug being released from adipose tissues of the chronic user. The confusional state may last 4–6 weeks. The condition may improve with time if phencyclidine exposure does not recur and if residual phencyclidine is excreted by acidifying the patient's urine.