A Trial of Guanfacine-er for Cannabis Use Disorder

Inclusion Criteria: * Meets DSM-V criteria for a current cannabis use disorder * Seeking treatment for cannabis use disorder with goal to reduce or stop use * THC-positive drug screen * Capable of giving informed consent and complying with study procedures * Access to internet and devices capable of completing study procedures * capability of receiving mailed packages for study supplies Exclusion Criteria: * Lifetime history of DSM-V diagnosis of schizophrenia or schizoaffective disorder * Current DSM-V criteria for a psychiatric disorder supported by the MINI that in the investigator's judgment is unstable, would be disrupted by the study medication, or is likely to require new pharmacotherapy or psychotherapy during the study period. Individuals who are currently stable on psychotropic medication for at least 2 months may be included if in the investigator's opinion the psychotropic medication is compatible with the study medication (guanfacine-ER). Any medical or psychiatric conditions that in the investigator's judgment would interfere with safe participation in the study will be exclusionary. * Individuals who meet DSM-V criteria for any moderate to severe substance use disorder other cannabis, caffeine or nicotine use disorders * Pregnancy, lactation, or failure to use adequate contraceptive method in female patients who are currently engaging in sexual activity that can result in pregnancy * Legally mandated to participate in a substance use disorder treatment program * Current or recent history of significant violent or suicidal behavior, risk for suicide or homicide * Known history of allergy, intolerance, or hypersensitivity to guanfacine * Bradycardia (\< 50 beats/minute), hypotension (sitting or standing BP \< 90/50), or symptoms attributable to hypotension (i.e. lightheadedness or dizziness on standing) * Individuals currently being treated with the antihypertensive medications, including the class of alpha 2 agonists that have a potential drug-interaction with guanfacine based on adrenergic modulation * Individuals currently taking medications that may interact adversely with guanfacine and deemed not clinically safe by study physician at consent, such as rifampicin, ketoconazole, St. John's Wort, and amitriptyline.