With exceptions (none of which seem to apply here), it's illegal to import a prescription drug into the U.S. unless the drug has been approved by the FDA. See:
https://www.fda.gov/aboutfda/transpa.../ucm194904.htm
I'm not a doctor and I'm no authority on Viagra, but:
"Pfizer, the manufacturer of erectile dysfunction med Viagra, just reached a settlement with generic manufacturer Teva that will allow Teva to start selling generic Viagra (sildenafil) in December 2017." See:
https://www.goodrx.com/blog/generic-...than-expected/
That would imply that there is presently not a generic for Viagra that currently can be legally imported into the U.S.
OP: You might read this, too:
http://www.consumerreports.org/presc...eneric-viagra/