I am a C4 Incomplete Tetra, I have heaps of hypo sensation and spasms which helps me to get erections.

Taking medication gives me much longer and harder erections which can last when needed sometimes over a 2 day period,

sometimes I get involuntary erections.
There will be so many variables in terms of age, health, how long since accident, how much sensation, level of injury etc, strength of med's.

It's never "cut & dry" my body has changed so much over 12 years, in the beginning only one medication worked, now they all seem to work at various degrees.
See your Urologist first

He should give you a prescription with various med's to trial.