ADL-5859, also known as compound 20, is an opioid drug that is selective for the ô-opioid receptor, it is being investigated as an alternative to traditional opioids in pain management.
Like all opioid drugs, ADL-5859 activates opioid receptors, but where as traditional opioids (such as oxycodone) activate the three main receptors (mu, delta, and kappa), ADL-5859 appears to be selective and only activates the delta receptor. with a K<sub>i</sub> of 20 nM
Like other opioids, it has potential in pain management; however, by being selective for the delta receptor, multiple undesirable side effects of traditional opioids are not present, such as respiratory depression, sedation, and euphoria.
ADL-5859 was also found to be orally active, which makes it easier to administer.
Multiple tests have shown its efficacy as an analgesic. It also did not seem to be a convulsant, unlike some other delta agonist opioids.