This article is from the Impotence FAQ, by Sine Nomine llama@drizzle.com with numerous contributions by others.
Definitely not. For the medication to work, it needs to be in the
spongy bodies along the sides of the penis, the corpora cavernosa. The
precise reason most doctors recommend that you inject on the side of
the penis is that injecting on the top makes hitting veins, arteries,
or nerves more likely. Injecting on the bottom puts you in danger of
injecting into the urethra, will which mean the shot is more or less
wasted.
 
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