The active ingredient, sildenafil citrate, is a PDE5 inhibitor. It works by blocking the enzyme phosphodiesterase type 5 (PDE5), which usually breaks down cyclic GMP, a substance responsible for relaxing the blood vessels in the penis. By inhibiting PDE5, sildenafil enhances the effect of nitric oxide, which allows blood vessels to relax, leading to increased blood flow to the penis and enabling an erection in response to sexual arousal.

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