The purpose of this study is to test the safety of an investigational medicine called ML-004 and how it might affect communication, behavior, and other symptoms of autism spectrum disorder (ASD). This medication is investigational because it has not been approved by the FDA for the treatment of symptoms associated with autism.

You may qualify if you:

• Are 12 to 17 years old
• Have an autism diagnosis
• Have a designated care/study partner able to attend every visit and answer questions about the participant. This person does not need to be the participant's parent or guardian. This person should have significant contact with them and can support them for the duration of the study.
• Are able to swallow the study medication (tablet)

The purpose of this study is to test an investigational medication in children and adolescents aged 5-17 years old with irritability associated with autism spectrum disorder (ASD). The name of the medication being tested in this study is pimavanserin. This medication is investigational because it has not been approved by the FDA for the treatment of irritability associated with autism. The main risks of this study are from the medication, which include nausea, dizziness, and sleepiness.