Rats display conditioned rejection reactions during an oral infusion of a flavor previously paired with an emetic drug; considerable evidence indicates that these rejection reactions reflect nausea. Here we report that cannabidiol, a major non-psychoactive cannabinoid found in marijuana and its synthetic dimethylheptyl homolog interfere with nausea elicited by lithium chloride and with conditioned nausea elicited by a flavor paired with lithium chloride. These results suggest that cannabinoids without psychoactive side-effects may have therapeutic value in the treatment of chemotherapy-induced nausea.