The main purpose of this study is to evaluate safety and tolerability in a subgroup of patients with Autism Spectrum Disorder (ASD). In addition, Pharmacokinetics and Pharmacodynamics, as well as efficacy of STP1 are being explored.

After obtaining written informed consent, those patients who are deemed eligible for the study, will be randomized on Day 1, in a double-blinded manner, in a 3:1ratio to receive either oral STP1 (twice daily) or placebo (twice daily). The total study duration is 6 weeks, including a screening phase of up to 2 weeks, a treatment phase of 2 weeks and a post-treatment follow-up phase of 2 weeks.

Key Inclusion Criteria:

1. Male or female individuals, between 18 and 40 years, diagnosed of ASD.
2. Patients will be assessed for specific developmental anthropometric & anatomical criteria as well as personal and family medical history as assessed by the ASD-Phen1 semi structured interview form.
3. Patients must have a parent or reliable caregiver who can provide information about the pre-natal period and early developmental period, as required by the protocol.
4. Patient and/or parent or legal guardian willing and consenting to participate.
5. Patients with ASD and comorbid seizure disorder should be seizure-free for at least 6 months prior to screening.
6. Before enrolling in the study, subjects must agree to use double-barrier birth control methods if they engage in intercourse.

Key Exclusion Criteria:

1. Patients with an identified genetic cause of ASD in their medical record will be excluded from the study.
2. History of traumatic head injury, cerebrovascular disorder, congestive heart failure, hepatic or renal disease.
3. Thrombocytopenia.
4. Type 1 Diabetes Mellitus or uncontrolled type 2 Diabetes Mellitus, or latent autoimmune diabetes of the adult.
5. A significant risk for suicidal behavior.
6. Initiation of, or a major change in psychological / behavioral intervention within 4 weeks prior to randomization.
7. Patient with any active infection.
8. Systolic blood pressure (SBP) <80 mmHg or diastolic blood pressure (DBP) <40 mmHg or a drop in SBP of ≥20 mm Hg, or in DBP of ≥10 mm Hg, during the orthostatic recordings.
9. Clinically relevant electrocardiogram (ECG) abnormalities.
10. Clinically significant abnormal laboratory test.
11. Active clinically significant disease.
12. History of malignancy.
13. Pregnant (confirmed by laboratory testing) or lactating female patient.

The total duration of the study for each participant was up to six weeks divided as follows: a screening phase of two weeks (from Day -14 to Day -1); a double-blind treatment phase of two weeks (from Day 1 to Day 14); and a follow-up phase of two weeks after treatment discontinuation (from Day 15 to Day 28).

As per ClinicalTrials.gov definitions.