RecruitingPhase 2Drug trialTrial of Diphenhydramine for Sleep in Children With AutismThe purpose of this study is to examine the effect of diphenhydramine on sleep in children and adolescents with Autism Spectrum Disorder (ASD). Diphenhydramine is an anti-histaminergic agent with strong hypnotic properties. To accomplish this, the investigators will use a randomized double-blind placebo-controlled crossover 8-week study design to examine the effect of diphenhydramine on sleep physiology as assessed by polysomnography (PSG), actigraphy, circadian rhythm, and clinical measures.