Clozapine is a drug commonly used in the treatment of schizophrenia. It has a sedative-hypnotic effect, but it is not used as a treatment for insomnia. Clozapine inhibits the brainstem upward reticular activation system and has a powerful sedative-hypnotic effect, which can produce the adverse effect of drowsiness. For insomnia caused by schizophrenia, clozapine can be used for treatment, but it needs to be used under the guidance of a psychiatric specialist. There are many causes of insomnia, most of which are due to emotional and psychological factors, such as anxiety, depression or short-term mental tension, excitement, and neurasthenia. They can also be seen in physiological insomnia, such as somatization disorders and gastrointestinal disorders, such as post-stroke sleep inversion, restless legs syndrome, and Parkinson’s disease, which are also common causes of insomnia and require symptomatic treatment for the cause of insomnia. Sedative-hypnotic drugs are all Class II psychotropic drugs, which need to be taken under the guidance of a specialist, and should never be taken on their own to avoid serious adverse reactions.