I'm not sure why acetaminophen is teamed with opioid type painkillers. I disagree that there is any proof of a "synergy" in pain relief, though the effect may be additive.
Personally, I find acetaminophen to be a weak, mediocre pain medication. And looking through the literature, I have not been able to find evidence that it matches any particular NSAID in dealing with pain.
HOWEVER, while I used to take Aleve routinely, I've encountered twenty plus years of literature showing that NSAIDs can actually delay healing, and therefore should be used very sparingly if at all by paddlers with aches and pains. Here's a lead in to the maze.
Chicago Sports Medicine - NSAIDs Hamper Ligament & Tendon Healing
"NSAIDs have been shown to delay and hamper the healing in all the soft tissues, including muscles, ligaments, tendons, and cartilage. Anti-Inflammatory medications can even significantly delay healing in muscle injuries with their tremendous blood supply. In one study on muscle strains, Piroxicam essentially wiped out the entire inflammatory proliferative phase of healing (days 0-4 post-injury). At day two, there were essentially no macrophages (cells that clean up the area) in the area. By the fourth day after the muscle strain there was very little muscle regeneration compared to the normal healing. The muscle strength at this time was only about 40 percent of normal."
I have also seen a study where young men with comparable shoulder injuries (rotator cuff)were put in matched groups. One group took an NSAID, the other got a placebo, and rehab routine was matched. Then the state of tissue healing was evaluated both with scans and "clinically." Those who had taken NSAIDs were significantly behind in healing.
One reason for this is that inflammation is an inherent part of the tissue healing process. NSAIDs interfere directly and specifically with the inflammation/healing mechanism. Reducing inflammation is NOT necessarily a good thing.
I don't know why this has not hit the NSAID warning labels up to now, or why many doctors and paddlers seem fuzzy on the issue.
Use NSAIDs for paddling pain only temporarily, with the goal of reducing pain that is directly keeping you from doing your everyday activities. Don't preload on NSAIDs. Don't take them routinely for paddling injury. (Some forms of arthritis are another matter.)
Sorry to spoil your day.