BMS 986188 is a positive allosteric modulator of δ-opioid receptors, with an EC value of 0.05 μM in a β-arrestin recruitment assay in the presence, but not absence, of the opioid receptor agonist leu-enkephalin . It is selective for δ- over μ-opioid receptors (EC = >10 μM) in the presence of leu-enkephalin and the μ-opioid receptor agonist endomorphin 1 , respectively.