Background and Purpose: Of the three primary cannabinoids in cannabis: 9-Tetrahydrocannabinol (9-THC), Cannabidiol (CBD) and Cannabinol (CBN), very little is known about the actions of CBN, the primary oxidative metabolite of THC. Our goal was to determine if CBN exposure during gastrulation alters embryonic development, and if so, via which cannabinoid receptors. Experimental Approach: Zebrafish embryos during the gastrulation stage (5-10.75 hpf) were exposed to CBN in the presence or absence of cannabinoid receptor blockers. We examined neuronal morphology, hair cell development and locomotion. Key Results: Embryos exhibited dose-dependent malformations in morphology, increased mortality, decreased locomotion and a reduction in motor neuron branching. Larva exhibited a significant reduction in the response to sound stimuli. CBN exposure altered the development of otic vesicles and hair cells associated with the lateral line. Pharmacological block of CB2Rs with AM 630 or JTE 907 prevented many of the CBN-induced developmental defects, while block of CB1Rs with AM 251 or CP 945598 had little or no effect. Conclusion and Implications: Altogether we show that embryonic exposure to CBN results in alterations in embryonic growth, neuronal and hair cell development, and physiology and behavior via CB2R-mediated mechanisms. Our results suggest that embryos exposed to CBN may be at an increased risk of abnormal development.