Picenadol is a 4-phenylpiperidine derivative and a racemic mixture whose mixed agonist-antagonist properties are a consequence of the d-isomer being a potent opiate agonist, whereas the I-isomer is an opioid antagonist. In the mouse writhing and rat tail heat tests, the analgesic potency of picenadol is estimated to be 1/3 that of morphine. Picenadol itself has weak antagonist activity, whereas the antagonist potency of the l-isomer is approx. 1/10 that of nalorphine. Picenadol has high affinity for both the mu and delta receptors but a markedly lower affinity for the kappa receptor. Extensive pharmacological investigations show picenadol to have a low potential to produce opiate-like side effects, including a low liability for abuse and physical dependence. Antinociceptive properties of picenadol arise from mu agonist actions of the dextrorotatory isomer and that the levorotatory isomer acts to limit the efficacy of the racemate.