Paroxetine hydrochloride is a serotonin uptake inhibitor that is effective in the treatment of depression. It is a highly potent and selective ST (serotonin transporter/5-HT) uptake inhibitor. It acts by binding to ST (serotonin transporter/SERT) with high affinity. Paroxetine binds to the pre-synaptic serotonin transporter complex resulting in negative allosteric modulation of the complex thereby blocking reuptake of serotonin by the pre-synaptic transporter. Paroxetine HCl has also displayed a high affinity for muscarinic acetylcholine receptors.