Penegra 50 mg typically starts working within 30 to 60 minutes after ingestion. Its effects can last for up to 4 to 6 hours, during which time a man may find it easier to achieve and sustain an erection when sexually aroused. Penegra 50 mg works by inhibiting the enzyme PDE5, which is responsible for degrading cyclic guanosine monophosphate (cGMP) in the penis. This inhibition leads to increased levels of cGMP, which relaxes the smooth muscles in the penile blood vessels, allowing increased blood flow into the penis during sexual stimulation.