5F-CUMYL-PINACA acts as a potent agonist for the cannabinoid receptors, with the original patent claiming approximately 4x selectivity for CB1, having an EC50 of <0.1 nM for human CB1 receptors and 0.37nM for human CB2 receptors. In more recent assays using different techniques, 5F-CUMYL-PINACA was variously found to have an EC50 of 0.43nM at CB1 and 11.3nM at CB2, suggesting a somewhat higher CB1 selectivity of 26x, or alternatively 15.1nM at CB1 and 34.8nM at CB2 with only 2.3x selectivity, however these figures cannot be directly compared due to the different assay techniques used in each case.