Composed Sildenafil citrate was originally developed by a major pharmaceutical group as a possible treatment for hypertension and other heart and circulatory problems.

During clinical trials the drug showed disappointing results in selected lung conditions set out, but an unexpected side effect that may be useful: erection of the penis.

The pharmaceutical company behind the original compound started to look Sildenafil as a treatment for erectile dysfunction. The patent followed in 1996 and once the FDA has approved its use for erectile dysfunction, in 1998, Sildenafil has become the first medical compound ED.

Patents held for Sildenafil were the source of much legal wrangling worldwide. In some countries Sildenafil is built without a licence because of local government policies.

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