Δ8-Tetrahydrocannabinol (Δ8-THC) is a naturally occurring cannabinoid with a characteristic pharmacological profile of in vivo effects. Previous studies have shown that modification of the structure of Δ8-THC by inclusion of a nitrogen-containing functional group alters this profile and may alkylate the cannabinoid receptor, similar to the manner in which β-funaltrexamine (β-FNA) alkylates the μ-opioid receptor. Two novel analogs of Δ8-THC were synthesized: a nitrogen mustard analog with a dimethylheptyl side chain (NM-Δ8-THC) and a cyano analog with a dimethylpentyl side chain (CY-Δ8-THC). Both analogs showed high affinity for brain cannabinoid receptors and when administered acutely, produced characteristic Δ9-THC-like effects in mice, including locomotor suppression, hypothermia, antinociception and catalepsy. CY-Δ8-THC shared discriminative stimulus effects with CP 55,940; for NM-Δ8-THC, these effects also occurred, but were delayed. Although both compounds attenuated the effects of Δ9-THC in the mouse behavioral tests, evaluation of potential antagonist effects of these compounds was complicated by the fact that two injections of Δ9-THC produced similar results, suggesting that acute tolerance or desensitization might account for the observations. NM-Δ8-THC, but not CY-Δ8-THC, attenuated the discriminative stimulus effects of CP 55,940 in rats several days following injection. Hence, addition of a nitrogen-containing functional group to a traditional cannabinoid structure does not eliminate agonist effects and may produce delayed attenuation of cannabinoid-induced pharmacological effects. © 1997 Elsevier Science Ltd. All rights reserved.