The inhibition of Serotonin uptake inhibits the ejaculatory expulsion of reflex to the brain, thereby preventing premature ejaculation in men.. Sildenafil prevents the destruction of an enzyme cGMP and allows cGMP to accumulate and persist longer. For ejaculation to happen in men, a reflex has to be passed on to the brain via the sympathetic nervous system. The longer cGMP persists, the more prolonged the engorgement of the penis The mechanism of action of Tadalafil is the same as sildenafil citrate Viagra (Sildenafil) and works by blocking an enzyme called PDE 5 which helps the smooth muscles in the penis to relax, thereby increasing blood flow to the penis. Dapoxetine belongs to a class of medicines known as Selective Serotonin Reuptake Inhibitors sildenafil citrate jelly 5 mg 20 sachets (SSRI) which inhibits the uptake of serotonin in the neural cells.