Cenforce 100 mg and Fildena 100 mg both contain sildenafil citrate, which improves blood flow to the penis, helping achieve and maintain an erection for about 4-6 hours. They are taken roughly an hour before sexual activity. Vidalista 20 mg contains tadalafil, which also enhances blood flow but has a longer-lasting effect, up to 36 hours. This extended duration allows for more flexibility in sexual activity and should be taken 30 minutes to an hour before sex.