Severe Disruptive Behaviour Disorders

The goal of this clinical trial is to learn if propranolol can help reduce challenging behaviors associated with Autism Spectrum Disorder, including aggression, self-injury, and severe disruptive behaviors. Participants will be randomly assigned to receive either propranolol or a placebo (a look-alike substance that contains no drug) daily for 12 weeks. After the 12 weeks, all participants will have the opportunity to receive propranolol for an additional 12 weeks.