Why Was the Atypical Antipsychotic Drug Clozapine Not Used Clinically

Why was the atypical antipsychotic drug clozapine not used clinically for schizophrenia until the 1970s and 1980s?

A) The high cost of its production caused mental health organizations to favor typical antipsychotics.
B) Its effectiveness went mostly unnoticed because it treats mostly negative schizophrenic symptoms.
C) It produced excessive extrapyramidal side effects until a new derivative was synthesized.
D) It was initially disregarded because of a lack of extrapyramidal side effects in animal models.