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There are a variety of treatment options available for pervasive developmental disorders such as autism. Although the exact cause of autism is unknown there are treatments for behaviors and symptoms associated with the condition. Risperdal is FDA approved for the treatment of Autism and is usually dosed at a starting dose of 2mg for adults and titrated upward from there. If your son responded well to 1mg I would encourage that you advocate for a dosage of 1mg if that is managing his symptoms. At increased doses Risperdal's side effect risks increase. These side effects can include akathesia (feelings of restlessness), low blood pressures, high blood sugars, increased risk of diabetes, dystonic reactions (condition where muscle involuntarily tighten) or neuroleptic malignant syndrome (life threatening condition with high body temperatures, muscle tightening, and possibly kidney failure from muscle tissue breakdown products overloading the kidneys). These side effects are rare but possible and increase with increased dose and prolonged duration of use. More common side effects include sedation, weight gain, dry mouth, constipation, and upset stomach. As a general rule, no one knows your son better than you do. It is important to have an open dialog with your psychiatrist about all medications that your son takes. Discuss risk and benefits of treatment and advocate for your son if you are uncomfortable with a medication. Also behavioral therapy, speech, occupational and sometimes physical therapy has been shown to be helpful in treatment of autism.
Thank you for your question and I hope this information will be helpful in your decision making process.