The cannabinoid CB 1 receptor-mediated modulation of g-aminobutyric acid (GABA) release from inhibitory interneurons is important for the integrity of hippocampal-dependent spatial memory. Although adenosine A 1 receptors have a central role in fine-tuning excitatory transmission in the hippocampus, A 1 receptors localized in GABAergic cells do not directly influence GABA release. CB 1 and A 1 receptors are the main targets for the effects of two of the most heavily consumed psychoactive substances worldwide: D 9 -tetrahydrocannabinol (THC, a CB 1 receptor agonist) and caffeine (an adenosine receptor antagonist). We first tested the hypothesis that an A 1 -CB 1 interaction influences GABA and glutamate release in the hippocampus. We found that A 1 receptor activation attenuated the CB 1 -mediated inhibition of GABA and glutamate release and this interaction was manifested at the level of G-protein activation. Using in vivo and in vitro approaches, we then investigated the functional implications of the adenosine-cannabinoid interplay that may arise following chronic caffeine consumption. Chronic administration of caffeine in mice (intraperitoneally, 3 mg/kg/day, for 15 days, 412 h before trials) led to an A 1 -mediated enhancement of the CB 1 -dependent acute disruptive effects of THC on a short-term spatial memory task, despite inducing a reduction in cortical and hippocampal CB 1 receptor number and an attenuation of CB 1 coupling with G protein. A 1 receptor levels were increased following chronic caffeine administration. This study shows that A 1 receptors exert a negative modulatory effect on CB 1 -mediated inhibition of GABA and glutamate release, and provides the first evidence of chronic caffeine-induced alterations on the cannabinoid system in the cortex and hippocampus, with functional implications in spatial memory.