tests have also been performed with the injection to treat priapism ( an erection that will not go down).
Phenylephrine as an injection:
https://en.wikipedia.org/wiki/Phenylephrine
Phenylephrine is used by urologists to abort
priapism. It is diluted with normal saline and injected directly into the
corpora cavernosa. The mechanism of action is to cause constriction of the blood vessels entering into the penis, thus causing decreased blood flow and relieving the priapism. An injection is given every 3–5 minutes. If priapism is not resolved in 1 hour, another form of therapy is considered.
[15]
http://www.sciencedirect.com/science/article/pii/S0022534701665753
"The effectiveness and complications of intracorporeal phenylephrine without aspiration or irrigation as a treatment for priapism were assessed."
other site about phenylephrine
https://www.ncbi.nlm.nih.gov/pubmed/7714971
now be it said. DONT INJECT PREP H INTO YOUR THINGY!.. the injections, I am sure are more pure and less diluted with other things..but I am sure that if you massage it in the skin down there.. might be as effective.
also as Pansey had said, its in cold medicines... so I am sure the effect is dose dependent, that if taken can also lead to shrinkage. but care should be taken if taking cold medicine that higher doses may cause heart problems and/or heart attack/stroke??.
all being said.. will it actually shrink everything? who can tell, unless you try it. I am skeptical about it.