IC50: 14 μM (human GAT-1), 39 μM (rat GAT-1), 58 μM (rat GAT-2), 119 μM (human GAT-3), 378 μM (rat GAT-3), 1870 μM (human BGT-3)

Guvacine hydrochloride is a potent inhibitor of GABA transporter, dispalys modest selectivity for cloned GABA transporters with IC ₅₀ s of 14 μM (human GAT-1), 39 μM (rat GAT-1), 58 μM (rat GAT-2), 119 μM (human GAT-3), 378 μM (rat GAT-3), and 1870 μM (human BGT-3). Guvacine has low affinity at hBGT-1 (IC ₅₀ >1 mM). Guvacine hydrochloride is a potent inhibitor of GABA uptake, but does not inhibit sodium-independent GABA binding, and is weak or inactive as a GABA receptor agonist. Guvacine inhibits the uptake GABA and β-alanine with IC ₅₀ s of 23 ± 2 μM, 66 ± 11 μM in the Cat spinal cord, and 8 ± 1 μM, 123 ± 28 μM in the rat cerebral cortex, respectively.