Sildenafil inhibits the PDE5 enzyme, which breaks down cyclic guanosine monophosphate (cGMP). Increased cGMP levels lead to relaxation of the smooth muscles in the corpus cavernosum and improved blood flow, facilitating an erection in response to sexual stimulation.Dapoxetine increases serotonin levels in the brain by inhibiting its reuptake. Elevated serotonin levels help delay ejaculation and improve control over the timing of ejaculation.