4-Me-PDTic is a potent and selective Kappa Opioid Receptor Antagonist. 4-Me-PDTic had a Ke = 0.37 nM in a [35S]GTPγS binding assay and was 645- and >8100-fold selective for the κ relative to the μ and δ opioid receptors, respectively. Calculated logBB and CNS (central nervous system) multiparameter optimization (MPO) and low molecular weight values all predict that 4-Me-PDTic will penetrate the brain and pharmacokinetic studies in rats shows that 4-Me-PDTic does indeed penetrate the brain.