The mechanism of action of selective serotonin and noradrenaline re-uptake inhibitors (SNRIs)

Depression is associated with reduced levels of the monoamines in the brain, such as 5-HT. The selective 5-HT and noradrenaline re-uptake inhibitors (SNRIs) are thought to restore the levels of 5-HT and noradrenaline in the synaptic cleft by binding at their re-uptake transporters preventing the re-uptake and subsequent degradation of 5-HT and noradrenaline. This re-uptake blockade leads to the accumulation of monoamines in the synaptic cleft and the concentration returns to within the normal range. This action of SNRIs is though to contribute to the alleviation of the symptoms of depression. In the presence of the SNRIs, small amounts of 5-HT and noradrenaline continue to be degraded in the synaptic cleft.