Zudena 100 mg contains sildenafil, which is the same active ingredient as in Viagra. Here's how it generally works: Onset of action: It usually starts working within 30 to 60 minutes after taking it. Peak effect: The maximum effect is often reached around 60 to 120 minutes. Factors affecting onset:  Zudena 100 mg it on an empty stomach usually makes it work faster; a heavy or fatty meal can delay absorption. Duration: Its effects typically last for 4 to 6 hours, although this can vary between individuals.  Sexual stimulation is required for it to work; it won’t cause an automatic erection. If you want, I can also explain why sometimes people feel it works faster or slower than expected.