Naltriben is a potent and selective antagonist for the delta opioid receptor, which is used in scientific research. It has similar effects to the more widely used ô antagonist naltrindole, but with different binding affinity for the ô<sub>1</sub> and ô<sub>2</sub> subtypes, which makes it useful for distinguishing the subtype selectivity of drugs acting at the ô receptors. It also acts as a ú-opioid agonist at high doses.