The power we’re using has not caused any tummy issues in either of our dogs.
I’ve used Glucosamine Chondroitin with 2 generations of dogs. The smallest was about 70 lbs. The largest is a 130 lb Newfie. From my observations it really helps. My Newfie wasn’t getting up easily, wasn’t interested in walks, stopped surfing the kitchen counters for crumbs (ok, that part I didn’t mind). On the supplement he bounces like a puppy, runs laps around the house, and takes full advantage of his size to pull bread off the counters.
The vet recommended starting with half doses and increasing to full after a few days. It does seem to cause loose stools for the first few days.
CostCo is another good source.