Ok guys...I'm asking this for a friend....I know I know "yea right". Looking at the side affects of Viagra suggests that it's use would compromise a pilots medical.

Does anyone know for sure? If so are there any other ED LEDs that can be used without affecting a medical?

Excellent question for your friends AME

From AOPA's Medical Section. Don't know if this applies to class 1 or not.

Trade Name FAA Allowed Drug Classification Treatment For FAA Allowed Based On Web Link Viagra
sildenafil
impotence therapy agent erectile dysfunction
6 hour wait before flying
status report and no adverse side effects

Unless you experience an erection lasting more than four hours.

There are other less "fun" side affects. Blue/blurry vision - or so I'm told.

An additional side effect (specific to pilot usage), is long-term use will make an individual taller.