The α2a-adrenergic agonist, lofexidine, reduced cannabis withdrawal-related sleep disruption in the laboratory, but side effects (e.g. fatigue, hypotension) limit its utility as a treatment for cannabis use disorder. This study tested the potential efficacy and tolerability of a daily bedtime administration of the FDA-approved α2a-adrenergic agonist, guanfacine, in a human laboratory model of cannabis use disorder. Daily, nontreatment-seeking cannabis smokers (13M, 2F) completed a within-subject study comprising two 9-day inpatient study phases. Each phase tested the effects of daily placebo or immediate-release guanfacine (2 mg) on cannabis intoxication (5.6 percent THC; 2 days), withdrawal (4 days of abstinence) and subsequent ‘relapse’ (3 days of cannabis self-administration). Ratings of mood, sleep, cardiovascular effects, food intake, psychomotor performance and cannabis self-administration were assessed. An outpatient phase preceded each inpatient phase for medication clearance or dose induction. Under placebo medication conditions, cannabis abstinence produced significant withdrawal, including irritability, sleep disruption and anorexia. Guanfacine reduced ratings of irritability and improved objective measures of sleep during cannabis withdrawal relative to placebo but did not reduce cannabis self-administration. Guanfacine was well tolerated with little evidence of fatigue and only small decreases in blood pressure: no dose was held due to hypotension. Thus, a single daily administration of guanfacine at bedtime improved sleep and mood during cannabis withdrawal relative to placebo. This positive signal supports further studies varying the guanfacine dose, formulation or frequency of administration, or combining it with other medications to increase the likelihood of having an impact on cannabis use.