Difference between Sildenafil and Sildenafil citrate?

Question

The data I found seems to show no difference between Sildenafil and Sildenafil citrate. But if they are the same things, why Pfizer use Sildenafil citrate instead of Sildenafil as their product Viagra?

Answer 1

Sildenafil citrate is the active ingredient of Viagra and Slidenafil. Viagra is the brand name only Pfizer can use, while Slidenafil is a generic brand name and it's cheaper than Viagra.