Determine if riluzole shows evidence of efficacy, safety, and tolerability targeting drug-refractory irritability (DRI) in persons with autism spectrum disorders (ASD).

A randomized, double blind, placebo-controlled, 12-week cross-over study (5-week treatment periods with 2-week washout) of adjunctive riluzole in 12 persons with ASD and DRI between the ages of 12 and 25 years.

Inclusion Criteria:

• Age ≥ 12 and < 26 years.
• Weight greater than 50 kg.
• Diagnosis of ASD
• Drug-refractory irritability, as defined as screening ABC Irritability subscale (ABC-I) score of ≥18 AND 1) failure of clinically adequate treatment trials of both aripiprazole and risperidone or 2) failure of at least three previous clinically adequate drug trials targeting irritability (one trial must include aripiprazole or risperidone), as confirmed by caregiver reports and medical record review when available.
• Stable dosing of all concomitant psychotropic medications (including those targeting irritability) for four weeks prior to screening visit and during the study.
• Presence of parent/guardian willing to serve as informant for behavioral outcome measures and shipping control sample for Extracellular Signal-Related Kinase biomarker (ERK) assay.

Exclusion Criteria:

• Current use of more than two concomitant psychotropic drugs targeting irritability.
• Current use of valproic acid.
• Current use of drugs with known interaction with riluzole
• Current use of drugs with concomitant glutamatergic or glutamatergic- modulating action medications.
• For female subjects of child bearing potential, a positive serum pregnancy test.
• History of pancreatitis.
• Hemoglobin less than or equal to 8.0 gm/dL.
• Neutropenia with absolute neutrophil count less than or equal to 1.0 K/mcL.
• Problems with kidney functioning, as assessed by lab work
• Any major chronic medical or chronic respiratory illness considered to be uncontrolled by the Principal Investigator.