Can difficulty urinating be caused by opiates?

Yes: Opioids such as hydrocodone, oxycodone & morphine are associated with urinary retention, constipation & dry mouth, among other side effects. While one can attempt to prevent and deal with the latter two issues, preventing & treating urinary retention is trickier. Best to avoid other anticholinergic medications if at all possible.

Yes!: It is a complicated explanation but when someone takes too many opiates (and each person's level is different depending on their tolerance) it basically causes the muscles that help the bladder expel the urine to become "lazy" and not respond as quickly and as forcefully as they normally do. Luckily, this is a temporary condition that goes away as the opiates clear out of the body.