Tapentadol has strong norepinephrine reuptake-inhibiting activity (blocked by α antagonists) and only modest μ-opioid receptor affinity. It is less effective than oxycodone in the treatment of moderate to severe pain but causes less gastrointestinal distress and nausea. Tapentadol has been implicated in the serotonin syndrome and should be used with caution in seizure disorders.