Inclusion Criteria:  Males and females aged 6 - 18 years of age;  DSM-5 diagnosis of intellectual disability (ID):  Full scale IQ < 70 on standardized cognitive assessment. Testing results must be sighted by the investigators and performed within two years of enrollment. In the event that records of prior testing are unavailable or the assessment was more than 2 years prior, IQ will be estimated using the Wechsler Abbreviated Scale of Intelligence-II. Deficit in adaptive function (basis for severity rating of ID in DSM-5) in at least one activity of life on the Vineland Adaptive Behavior Scales (derives scores in Communication, Daily Living Skills and Socialization domains, and a Global Adaptive score). If records of prior testing are unavailable or the assessment was more than 2 years prior, this will be completed by the parent or guardian.  SBP: Defined as scores of:  18 or higher on the Aberrant Behavior Checklist-Irritability subscale (ABC-I), and moderate or higher on the Clinical Global Impressions-Severity scale; No changes in either medication or other interventions in the 4 weeks prior to randomization, and intention to remain on same dose for the duration of the study; Written informed consent from parent or legal guardian; Participant and family have the ability to comply with the protocol requirements, in the opinion of the investigator.  Exclusion Criteria:  Non-English speaking parents; Psychosis, bipolar disorder, major depressive disorder, obsessive compulsive disorder; Taking clobazam; Abnormal liver function tests: defined as ALT > twice ULN; Current use of medicinal cannabis, or use in the 4 weeks prior to screening; Pregnant or intending to become pregnant during the study, or breastfeeding; Known allergy to cannabidiol or cannabis products