Shifting Brain Excitation-Inhibition Balance in Autism Spectrum Disorder

Inclusion Criteria: * men * pass diagnostic threshold for ASD on the ADI-R (if informant is available) * currently symptomatic on ADOS * age 18-50 years * can give informed consent * IQ\>70 (on a standard instrument such as WASI) * medication-free in the month preceding participation (but regular medication with drug, which does not affect glutamate or GABA directly may be permitted) * willing to provide urine samples to screen for use of illicit substances prior to each scan Exclusion Criteria: * IQ\<70 * history of psychosis, co-morbid major mental illness, significant physical illness (heart disease, high blood pressure, seizures) * habitual substance misuse (including alcohol) * known allergy to cannabis * ASD caused by a known genetic syndrome e.g. Fragile X or 22q11 deletion syndrome, * past/present treatment for epilepsy * Women will be excluded from this pilot study to reduce heterogeneity in a small sample; avoid the issues around exposing women of reproductive age to a drug; and because pregnancy is a routine exclusion criteria for research MRI. Lastly, ASD is more common in men.