The psychoactive plant cannabinoid, Delta9-tetrahydrocannabinol, is antagonized by Delta8- and Delta9-tetrahydrocannabivarin in mice in vivo. 03 Jun Dr D Synthetic and plant-derived cannabinoid receptor antagonists show hypophagic properties in fasted and non-fasted mice. Antitumor activity of plant cannabinoids with emphasis on the effect of cannabidiol on human breast carcinoma.