Phenibut also binds to and blocks α2δ subunit-containing VDCCs, similarly to gabapentin and pregabalin, and hence is a gabapentinoid. Both (R)-phenibut and (S)-phenibut display this action with similar affinity (Ki = 23 and 39 μM, respectively). Moreover, (R)-phenibut possesses 4-fold greater affinity for this site than for the GABAB receptor (Ki = 92 μM), while (S)-phenibut does not bind significantly to the GABAB receptor (Ki > 1 mM). As such, based on the results of this study, phenibut would appear to have much greater potency in its interactions with α2δ subunit-containing VDCCs than with the GABAB receptor (between 5- to 10-fold). For this reason, the actions of phenibut as a α2δ subunit-containing voltage-gated calcium channel blocker or gabapentinoid may be its true primary mechanism of action, and this may explain the differences between phenibut and its close relative baclofen (which, in contrast, has essentially insignificant activity as a gabapentinoid; Ki = 6 μM for the GABAB receptor and Ki = 156 μM for α2δ subunit-containing VDCCs, or a 26-fold difference in affinity).