Cenforce 25 mg contains sildenafil citrate, a phosphodiesterase type 5 (PDE5) inhibitor. Sildenafil works by inhibiting the PDE5 enzyme, which increases levels of cyclic guanosine monophosphate (cGMP). This leads to the relaxation of smooth muscle in the blood vessels of the penis and enhanced blood flow, allowing for an erection in response to sexual stimulation.