A Study to Evaluate ARD-501 in Patients With Autism Spectrum Disorder

Inclusion Criteria: Subjects must meet all the following criteria to be eligible for participation in this study: * Male and female subjects, 17-30 years of age * Able and willing to sign consent and comply with study protocol * Diagnostic confirmation of ASD as confirmed by gold standard clinical interview using Diagnostic and Statistical Manual of Mental Disorders 5th Edition (DSM-5) criteria and administration of the Autism Diagnostic Observation Schedule-2, Module 3 or 4. * General good health as determined by physical exam, medical and psychiatric history and safety labs as defined by the Principal Investigator or designee. * Male study participants who are sexually active with a female partner of childbearing potential must be surgically sterilized, or agree to use highly effective methods of birth control (defined below), and not rely on barrier methods and spermicide alone, from the time of screening until 1 week after final dose of study drug. * Female participants of childbearing potential may be included in the study provided that they choose an effective contraception method that: 1) is not user dependent as permanent sterilization, intrauterine devices, and implants); or 2) is a user dependent short-acting hormonal method of contraception (e.g.injection, oral, transdermal, and intravaginal). Exclusion Criteria: Subjects who meet any of the following criteria will be excluded from study participation: * Allergy or hypersensitivity to ARD-501. * Inability to swallow study drug. * Unstable dosing of any mood, anxiety or behavior medications in 4 weeks prior to baseline visit. * Concomitant use of scheduled benzodiazepines, baclofen, gabapentin, pregabalin, or supplements with impact on the γ-aminobutyric acid (GABA) system. * Concomitant use of any cannabinoid or related product. * Any use of opioid medication * Unstable seizure disorder as defined by any seizure in the 6 months prior to baseline visit and/or a change in any anti-convulsant drug dosing in the 60 days prior to study screen. * Abnormal baseline safety lab assessments including, but not limited to alanine transaminase (ALT) or aspartate aminotransferase (AST) greater than 1.5x the upper limit of normal, total bilirubin or creatinine greater than 1x the upper limit of normal, other clinically relevant lab abnormality, or abnormality in electrocardiogram (ECG), heart rate (HR), or blood pressure (BP) at screening as determined by the investigator or designee. * History of or current abuse of drugs or alcohol including prescription medication. * Women who are pregnant (i.e., have a positive pregnancy test), intending to become pregnant, breast feeding, or women of child-bearing potential who are unwilling to use contraception as required in the study inclusion criteria or maintain abstinence during the course of the study * Inability to attend scheduled study visits, plans for family relocation during the study, or any other criteria that the investigator may determine to be associated with inability to complete the study * History of major depressive disorder or history of other severe psychiatric disorders (e.g., schizophrenia or bipolar disorder) within the last 2 years. * Suicidal ideas and behavior as assessed by the Columbia suicide severity scale (C-SSRS) * Consumption of more than 2 units (males) or 1 unit (females) per day of alcohol during the study * Any condition(s), including psychiatric disorders such as, but not restricted to bipolar disorders, that the investigator or primary physician believes may not be appropriate for participating the study * Patients weighing more than 275 lb (124.7 kg)