Description An opioid analgesic derived from morphine and used mainly as an analgesic. It has a shorter duration of action and is more potent than morphine. Mechanism of action Hydromorphone is a narcotic analgesic- its principal therapeutic effect is relief of pain. Hydromorphone interacts predominantly with the opioid mu-receptors. These mu-binding sites are discretely distributed in the human brain, with high densities in the posterior amygdala, hypothalamus, thalamus, nucleus caudatus, putamen, and certain cortical areas. They are also found on the terminal axons of primary afferents within laminae I and II (substantia gelatinosa) of the spinal cord and in the spinal nucleus of the trigeminal nerve. In clinical settings, Hydromorphone exerts its principal pharmacological effect on the central nervous system and gastrointestinal tract. Hydromorphone also binds with kappa-receptors which are thought to mediate spinal analgesia, miosis and sedation.