Background Dravet syndrome (DS) is one of the most severe forms of drug-resistant epilepsy and available interventions fail to control seizures in most patients. Cannabidiol (CBD) is the first in a new class of antiepileptic drugs with a distinctive chemical structure and mechanism of action. Objective The aim of this systematic review was to evaluate the efficacy and safety of CBD as adjunctive treatment for seizures in patients with DS using meta-analytical techniques. Methods We searched for randomized, placebo-controlled, single- or double-blinded trials. Main outcomes included >= 50% reduction in baseline convulsive seizure frequency and the incidence of treatment withdrawal and adverse events (AEs). Risk ratios (RRs) with 95% confidence intervals (95% CIs) were estimated through the inverse variance method. Results Three trials were included involving 359 participants, 228 for CBD and 131 for placebo groups. In all trials, the active treatment was a plant-derived pharmaceutical formulation of purified CBD oral solution. The pooled RR for 50% response during the treatment was 1.69 (95% CI 1.21-2.36; p = 0.002). Across the trials, treatment was discontinued in 20 (9.0%) and 3 (2.3%) cases in the add-on CBD and placebo groups, respectively; the RR for CBD withdrawal was 3.12 (95% CI 1.07-9.10; p = 0.037). The RR to develop any AE during add-on CBD treatment was 1.06 (95% CI 0.87-1.28; p = 0.561). AEs significantly associated with adjunctive CBD were somnolence, decreased appetite, diarrhea, and increased serum aminotransferases. Conclusions Adjunctive CBD resulted in a greater reduction in convulsive seizure frequency than placebo and a higher rate of AEs in patients with DS presenting with seizures uncontrolled by concomitant antiepileptic therapy.