This article is from the Impotence FAQ, by Sine Nomine llama@drizzle.com with numerous contributions by others.
The most common side effect is mild to moderate pain after injection
(although in the approval studies for Caverject, only 3% of
participants dropped out because of this). Priapism, an erection that
will not go away after more than six hours, is a fairly rare side
effect and may be dose-related. If you experience, this, it's
essential that you contact a doctor immediately. Read Jerry's post
about a seven-hour erection if you think priapism is no big deal.
Prolonged use of injectables may result in scarring, but as of yet
there isn't enough data to determine what the risk factors for this
are.
 
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