Pimavanserin is an antipsychotic may have some beneficial effects on core autism symptoms and co-morbid conditions such as irritability, anxiety, sleep disorders, mood instability due to epilepsy, etc.). These potential benefits stem from pimavanserin's impact on the serotonin system in the body. This study will investigate pimavanserin in the treatment of irritability, core autism symptoms, and co-morbid conditions in children ages 6-17 years old.