A selective antagonist of NMDA receptors that contain NR2B subunits (IC50 = 0.3 μM) with 150-fold weaker activity at those bearing NR2C or NR2D subunits; also acts as a potent ligand at receptors for σ1, emopamil binding proteins, and their σ-like, fungal counterpart ERG2 (Kis = 2, 5, and 1 nM)