Dopamine is a chemical messenger in the brain. It helps to do movements, release hormones and strengthen cognitive abilities. Researchers found that increasing the amount of dopamine in the brain will worsen the symptoms of autism. Substances that help to reduce symptoms of autism are the antipsychotic drugs. There are two types of antipsychotic medications. One of the types is typical antipsychotics. They block the sites where dopamine would bind to a cell. Atypical antipsychotic drugs block the sites where dopamine or serotonin would bind to a cell. Antipsychotic medicine is the most successful treatment for excitability in autism. It can also help to reduce aggression, self-injury, hyperactivity and repetitive behaviours, although it may have many side-effects. Originally, antipsychotic medications were used to treat mental disorders like depression, bipolar disorder or schizophrenia. Examples of antipsychotic drugs are Haloperidol, Clozapine, Risperidone and Paliperidone.