Being on the high dose of
Norco's that I was on, I noticed the same thing in regards to urination. It didn't hurt me at all BUT, the urine didn't come out like it used to before my narcotic addiction. It didn't trickle but it took a little longer to finish.
According to "The Pill Book 10th Edition", urinary difficulty is a "less common" side effect. It doesn't describe the actual symptoms of this (i.e pain, trickling....).
I would imagine the pain that he is having is caused by one of the other issues (agreeing with jgcmd) but the best thing would be to ask his doctor.
J
J