Penegra 100 mg is a medication used to treat erectile dysfunction (ED), and it contains sildenafil citrate, the same active ingredient found in Viagra. Sildenafil is a PDE5 inhibitor (phosphodiesterase type 5 inhibitor), and its main function is to increase blood flow to the *****, helping men achieve and maintain an erection during ***** activity. The reason Penegra 100 mg lasts only a few hours (typically 4-6 hours) is due to the way sildenafil is metabolized in the body and how it works at the biochemical level. Mechanism of Action: PDE5 Inhibition: When you take Penegra, sildenafil works by blocking the enzyme PDE5 in the blood vessels of the *****. PDE5 is responsible for breaking down a molecule called cGMP (cyclic guanosine monophosphate), which helps relax the smooth muscle cells in the blood vessels. When PDE5 is inhibited, cGMP levels increase, leading to the relaxation of the blood vessels and improved blood flow to the *****. ***** Stimulation Required: It’s important to note that sildenafil doesn’t cause an erection on its own. ***** arousal and stimulation are still required for an erection to occur. Sildenafil enhances the natural physiological response to ***** stimulation. Why It Lasts a Few Hours: Half-Life of Sildenafil: The half-life of sildenafil (the time it takes for half of the drug to be eliminated from the body) is about 4 hours. This means that Penegra 100 mg will remain effective for approximately 4-6 hours before it begins to lose its effectiveness.