This is a double-blind, randomised, placebo-controlled study investigating the efficacy of a full-spectrum medicinal cannabis plant extract on core and associated ASD symptoms over placebo. Participants will be randomly allocated to either NTI164 or placebo at a 1:1 ratio and blood samples will be collected and surveys completed at baseline and Week 16. This study will expand efficacy and safety data of NTI164 and provide additional mechanism of action data of NTI164 in this patient cohort.

Participants will be recruited from Monash Health, Vic, Australia and will have a diagnosis of ASD Level II or III, as well as satisfying other inclusion/exclusion criteria. The primary objective is to assess efficacy of 16 weeks of daily oral administration of NTI164 on core ASD symptoms compared to placebo. The secondary objectives are to further expand the safety data of NTI164 in this patient cohort, and assess the changes in other associated symptoms of ASD following NTI164.

Inclusion Criteria:

1. Participant is aged 6 years to 25 years (inclusive).
2. Participant is at a healthy weight at the discretion of the Principal Investigator.
3. Written informed consent from parent or legal guardian according to the local law.
4. Participants can comply with trial requirements.
5. According the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) criteria the participant has a diagnosis of Level II or III ASD confirmed by a validated assessment tool.
6. All treatments including medications and therapies for ASD related symptoms must have been stable for 12 weeks before enrolment and for the duration of the trial wherever possible.
7. Participants must be able to swallow liquid.
8. Consent giver must be able to understand the requirements of the study.

Exclusion Criteria:

1. Current diagnosis of bipolar disorder, psychosis, schizophrenia, schizoaffective disorder, or active major depression.
2. Has a diagnosis other than ASD that dominates the clinical presentation (e.g., ADHD).
3. Has a degenerative condition.
4. Changes in anticonvulsive therapy within the last 12 weeks.
5. Taking omeprazole, lansoprazole, tolbutamide, warfarin, sirolimus, everolimus, temsirolimus, tacrolimus, clobazam, repaglinide, pioglitazone, rosiglitazone, montelukast, bupropion, or efavirenz.
6. Currently using or has used recreational or medicinal cannabis, cannabinoid-based medications (including Sativex®, or Epidiolex®) within the 12 weeks prior to screening and is unwilling to abstain for the duration of the trial.
7. Participant has any known or suspected hypersensitivity to cannabinoids or any of the excipients.
8. Participant has moderately impaired hepatic function at screening, defined as serum alanine aminotransferase (ALT) or aspartate aminotransferase (AST) > 2 × upper limit of normal (ULN) or total bilirubin (TBL) > 2 × ULN. This criterion can only be confirmed once the laboratory results are available; participants enrolled into the trial who are later found to meet this criterion must be screen-failed.
9. Participant is male and fertile (i.e., after puberty unless permanently sterile by bilateral orchidectomy) unless willing to ensure that they use male contraception (condom) or remain sexually abstinent during the trial and for 12 weeks thereafter.
10. Participant is female and with childbearing potential (i.e., following menarche and until becoming postmenopausal for ≥ 12 consecutive months unless permanently sterile by hysterectomy, bilateral salpingectomy, or bilateral oophorectomy) unless willing to ensure that they use a highly effective method of birth control (e.g., hormonal contraception, intrauterine device/hormone-releasing system, bilateral tubal occlusion, vasectomised partner, sexual abstinence) during the trial and for 12 weeks thereafter.
11. Female participant who is pregnant (positive pregnancy test), lactating or planning pregnancy during the course of the trial or within 12 weeks thereafter.
12. Participant had brain surgery or traumatic brain injury within 1 year of screening.
13. Participant has any other significant disease or disorder which, in the opinion of the Investigator, may either put the participant, other participants, or site staff at risk because of participation in the trial, may influence the result of the trial, or may affect the participant's ability to take part in the trial.
14. Any abnormalities identified following a physical examination of the participant that, in the opinion of the Investigator, would jeopardise the safety of the participant if they took part in the trial.
15. Any history of suicidal behaviour (lifelong) or any suicidal ideation of type 4 or 5 on the Columbia-Suicide Severity Rating Scale (C-SSRS) in the last 12 weeks or at screening or randomisation.
16. Participant has donated blood during the past 12 weeks and is unwilling to abstain from donation of blood during the trial.
17. Participant has any known or suspected history of alcohol or substance abuse or positive drugs of abuse test at screening (not justified by a known concurrent medication).
18. Participant has previously been enrolled into this trial.
19. Participant has plans to travel outside their country of residence during the trial, unless the participant has confirmation that the product is permitted in the destination country/state.

All study team members will be blinded during the main treatment phase of this study (i.e up to Week 16). Only Clinical Trial Pharmacy staff will be unblinded.