We found this review to be quite old but its still may be quite up to date
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Viagra and how to use it – personal experience
The first time I took Viagra I broke all my own rules for trying out a new drug (except that I got it from someone I trusted not to poison me). Normally I would have gone to one of the drug resource sites and read up on proper dosage and other details to help me get the most out of the experience. Then I would have talked with more experienced friends to see how it worked for them. What happened instead is that an older friend of mine, who actually had “erectile dysfunction” and was prescribed Viagra, gave me one of his pills and said, “Try it.” So I did.