Clozapine is not normally associated with tardive dyskinesia (TD) and is recommended as the drug of choice when this is present, although some case reports describe clozapine-induced TD. Other serious risks include seizures, inflammation of the heart, high blood sugar levels, constipation. The use of this drug can rarely result in clozapine-induced gastric hypomotility syndrome which may lead to bowel obstruction and death, and in older people with psychosis, as a result of dementia it may lead to an increased risk of death. The mechanism of action is not entirely clear in the current medical literature. Clozapine is on the World Health Organizations List of Essential Medicines. It is available as a generic medication. History
Clozapine was synthesized in 1958 by Wander AG, a Swiss pharmaceutical company, based on the chemical structure of the tricyclic antidepressant imipramine. The first test in humans in 1962 was considered a failure. Trials in Germany in 1965 and 1966 as well as a trial in Vienna in 1966 were successful. In 1967 Wander AG was acquired by Sandoz. Further trials took place in 1972 when clozapine was released in Switzerland and Austria as Leponex. Two years later it was released in West Germany and in Finland in 1975. Early testing was performed in the United States around the same time. In 1975,  16 cases of agranulocytosis leading to 8 deaths in clozapine-treated patients, reported from 6 hospitals mostly in southwestern Finland, led to concern.
In Pratt VM, McLeod HL, Rubinstein WS,  et al. (eds.). Medical Genetics Summaries. National Center for Biotechnology Information (NCBI). PMID 28520348. Bookshelf ID: NBK100660. External links
"Mercaptopurine". Drug Information Portal. U.S. National Library of Medicine.