Do collagen tablets decrease healing time after a shoulder operation?

We just don't know. There are no well controlled double blinded crossover studies in humans to prove that collagen supplements work any better than placebo. Knox gelatin powder may work as well for shoulder injury as any supplement being sold online or at your corner health food store. Most hydrolyzed collagen comes from cattle, pig, fish, and hoses byproducts, so watch for food allergies. Vegans beware!