"Sometimes you have to take some things that give you a little bit of relief," he told Newstalk ZB. "But you don't want to live on those, either - that's not how sport's meant to be played.
"But sometimes you do suffer injuries and there's stiffness and soreness, and you have to take painkillers to be able to get out there and play. I'm certainly not advocating for everyone to follow that sort of script but, at this stage, I'm a bit stiff and sore so you take some mild medicine to get you out there."
After a 12-month stretch as intense as any he's experienced, McCullum's discomfort is understandable. Performing with his brand of aggression would certainly take its toll, particularly when any new problems are piling on top of the long-standing issues he has faced in the latter years of his career.
"There's times when you feel physically at the top of your game," he said. "Then there's times when you might take a fall in the field, or you might have a fairly intense travel schedule, or you might suffer a slight niggle during the game.
"Obviously with pre-existing injuries you're always susceptible for that. I've got my injuries but every player does. It's just about trying to manage those and still be comfortable that you're fit enough to go out there and perform."
As part of that management, McCullum will sit out the forthcoming short-form series against South Africa and Zimbabwe, enjoying a well-earned break and leaving Kane Williamson to lead the team.
The rest will ensure McCullum is fit and firing for the home-and-away test series against Australia this summer, but there is another motivation fuelling the desire to look after his body.
"You don't want to finish your career and not be able to chase your kids around the park," he said. "There's a fine line there. But if I didn't think that I was going to be fit and strong enough to be able to get through the next 12 months, then I wouldn't have committed."
The commitment will see McCullum, health willing, become the first cricketer to play 100 successive tests following his debut. While driven by more than than personal milestones, McCullum admitted achieving the feat would be a fitting way to bow out of the international game, though he left open the possibility of adding another year to his considerable legacy.
McCullum has already helped change the way cricket is played, with run rates sky-rocketing and bat consistently dominating ball. And the ICC today approved several rule changes to balance the scales in ODIs, with the batting powerplay jettisoned and an extra fielder now allowed outside the 30-yard circle in the final 10 overs of an innings.
