Yes Dani, we've been using the stuff on dogs and horses for years now. (With great benefit) I'll let you in on the secret I told John, TALK TO YOUR VET!!! We sell huge 4lb buckets of synoflex/equi-flex/whatever for horses, with the dosages modified for dogs. All of the human runners in our clinic use the stuff as well. It comes in a powdered for for use in sprinkling over horse feed, but a spoonfull mixed in OJ or chocolate milk and you can't tell. Anyhow, the buckets are a lot cheaper than anything humans can shove into a pill form, and it is the same supplements. Only advice is to NOT take MSM while taking Vitamin C supplements. The onlt real side-effect with MSM/C is that you'll be glad you are a runner when it comes time to make tracks for the bathroom....
Happy Trails,
~Jen