Tramadol is a centrally acting analgesic that binds to the µ-opioid receptor. The drug undergoes extensive metabolism via CYP450 2D6, leading to an active metabolite that has a much higher affinity for the µ receptor than the parent compound. In addition, it weakly inhibits reuptake of norepinephrine and serotonin. It is used to manage moderate to moderately severe pain. Its respiratory-depressant activity is less than that of morphine.