Knowing the mechanism is very important before you buy Ultram online. Ultram, a centrally acting -opioid receptor agonist and SNRI (serotonin/norepinephrine reuptake inhibitor), and the medicines codeine and morphine have structural similarities. Compared to morphine, Ultram has an affinity for the -opioid receptor that is 6000 times lower, and it barely interacts with the - and -opioid receptors. The opioid receptor is activated by (+)-Ultram and (+)-O-desmethyl-Ultram (M1), while (+)-Ultram inhibits serotonin reuptake and (-)-Ultram inhibits norepinephrine reuptake. Ultram is a racemic combination of these two pharmacologically active enantiomers. The synergistic interplay of these systems improves Ultram's ability to modulate pain perception and responsiveness.