All Viagra is the same — powered by the same active ingredient, Sildenafil. These are commonly prescribed for an enlarged prostate or male pattern baldness. This works in a similar way to Viagra , but its effects last for longer. In human clinical trials, however, sildenafil caused an unexpected side effect: the dilating blood vessels were in the penis, not the heart. It works for up to 36 hours. It tends to be recommended to those who have tried Viagra Connect but have not seen results. This is a drug known as a PDE5 inhibitor.What’s the best Viagra for men? That will depend entirely on you. While most men start with the 50mg option — known as Viagra Connect — others will find that .  · a light-headed feeling, like you might pass out. Common sildenafil side effects may include: flushing (warmth, redness, or tingly feeling); headache, dizziness; . It really depends based on the person. Most of the time, Viagra starts to work after 30 minutes. Some people note that Viagra works faster when taken on an empty stomach. The effects of Viagra usually last around 4 to 5 hours, in which time it is easier to have an erection. But in some cases, this window of time See more.