When Kids Need Meds: Everything a Parent Needs to Know About Psychiatric Medication and Youngsters. (2012) Henry A. Paul, M.D. Available for $2.99 to read on Amazon Kindle, free to Kindle Unlimited subscribers, and available from amazon.com in paperback for $11.58.
Child and Adolescent Clinical Psychopharmacology Made Simple by John Preston, Psy.D., ABPP; John H. O'Neal, MD,; and Mary C. Talaga, R.Ph., Ph.D. (available on amazon.com).
http://www.ncbi.nlm.nih.gov/pubmed/8935208 --Fluoxetine (Prozac) alleviated symptoms of selective mutism (a severe anxiety disorder where the child is able to speak but basically appears mute in social situations) in 76% of the kids in the study. Social anxiety disorder is over-represented in kids with autism. A high percentage of kids with selective mutism also have speech disorders.
http://www.youtube.com/watch?v=GZVJbXe1nKg --Child psychiatrist explains giving medication for irritability, focusing on Risperidal and Abilify, which are FDA approved for this purpose. Easy to understand. Please see the other links for other medication options that may work better for your child and might produce fewer side effects.