Tramadol is opioid

Opioid activity of tramadol is caused by both low affinity binding from the parent compound and affinity binding of the O-demethylated metabolite M1 to µ-opioid receptors. In animal models, M1 is about 6 times tougher than tramadol in producing analgesia and 200 times tougher in µ-opioid binding. Tramadol-induced analgesia is merely partially antagonized through the opioid antagonist naloxone in a number of animal tests. The relative contribution of both tramadol and M1 to human analgesia will depend on the plasma concentrations of each and every compound.