Zenegra 50 mg (sildenafil 50 mg) usually becomes ineffective about 4–6 hours after a dose; its peak effect occurs ~30–60 minutes after taking it and sexual stimulation is required for it to work. How it behaves and why: Onset: It typically starts working within 30–60 minutes after ingestion, though a heavy fatty meal can delay this. Duration: Most users have useful effect for about 4 hours (some report up to 6 hours), after which the drug’s blood levels fall and it is unlikely to help with erections. Practical notes: If you wait too long after taking it, or you haven’t used enough dose, or you’re not sexually aroused, it may seem ineffective. One short example:  Zenegra 50 mg about 1 hour before sex, avoid large fatty meals and alcohol, and expect reliable effect primarily within the next 4 hours. If it stops working or works less well than before, talk with your doctor — causes include dose, interactions, health conditions, or psychological factors and a clinician can adjust therapy safely.