Understanding Effects of Cannabis Use and Abstinence on Neural Glutamate Homeostasis

Inclusion Criteria: HC and CUD Group: * Voluntary, written, informed consent * Physically healthy by medical history, physical, neurological, ECG and laboratory exams * No personal or first-degree relative history of psychiatric disorders (outside of cannabis use for CUD group) * Full scale and verbal IQs \> 80 (Wechsler Adult Intelligence Scale, Fourth Edition; WAIS-IV). CUD group: * Cannabis use disorder as determined by DSM-5 structured interviews * Urine toxicology evidence of cannabinoid use HC group: * lifetime cannabis exposure less than 20 times * no cannabis use in the past 2 years by self-report * a negative urine drug screen. Exclusion Criteria: * Other substance use disorder within 1 year, except for nicotine * Another primary DSM-5 Axis I major psychiatric disorder (e.g., schizophrenia, bipolar disorder, major depression, etc.) per SCID-5 * Urine toxicology results positive for other drugs such as opiates / opiate metabolites (e.g., methadone, buprenorphine, etc.) * A history of significant medical (cardiac, infectious, metabolic) or neurological illness (e.g., cerebrovascular disease, traumatic brain injury) * A history of seizures/epilepsy * Current use of psychotropic and/or potentially psychoactive prescription medications * Medical contraindications to MRI imaging (e.g., ferromagnetic implants/foreign bodies, claustrophobia, etc.) * Pregnancy or breastfeeding (women). * Subjects will be excluded for major medical or neurological illness or laboratori…