The active substance in Yentreve, duloxetine, is a serotonin-noradrenaline re-uptake inhibitor (SNRI). It works by preventing the neurotransmitters 5-hydroxytryptamine (also called serotonin) and noradrenaline from being taken back up into nerve cells in the brain and spinal cord.

Neurotransmitters are chemicals that allow nerve cells to communicate with one another. By blocking their re-uptake, duloxetine increases the amount of these neurotransmitters in the spaces between these nerve cells, increasing the level of communication between the cells. How duloxetine works in SUI is not clear but it is thought that, by increasing the levels of 5-hydroxytryptamine and noradrenaline at the level of the nerves that control the muscle of the urethra (the tube that leads from the bladder to outside), duloxetine causes a stronger closure of the urethra during urine storage. By closing the urethra more powerfully, Yentreve prevents the unwanted loss of urine during physical stress such as coughing or laughing.