("R")-Phenibut and ("S")-phenibut have been assayed at 85 binding sites at a concentration of 100 μM with no activity (less than 20% inhibition of binding) observed except at the α2δ VDCC subunit and the GABAB receptor. In this study, ("R")-phenibut and ("S")-phenibut showed IC50 values for inhibition of gabapentin binding of 87.1 μM and 91.0 μM (Ki = 60 μM), respectively. The IC50 for gabapentin under the same conditions was 0.09 μM. The researchers also assessed phenibut at the GABAB receptor and found a Ki value of 57 μM for ("R")-phenibut, which would be about twice that concentration (~114 μM) with racemic phenibut.