In case you have not heard, use of Viagra raises the risk for developing melanoma. In fact the risk for melanoma almost doubles compared with those who do not use Viagra. This should prompt a yearly skin exam by a dermatologist. Those with a personal or family history of melanoma might even consider discontinuing the medication.
You can read more about this increased risk here:
http://www.medpagetoday.com/HematologyOncology/SkinCancer/46153