Another tremendously helpful gathering of the data (and lack thereof) on dietary supplements for dogs & cats, via SkeptVet:
From Science-Based Medicine: The Top Ten Pet Supplements–Do They Work?
…Much has been written here about the dietary supplement industry, a multibillion dollar industry with powerful political connections, and about the woeful inadequacy of regulation which allows widespread marketing of supplements without a solid basis in science or scientific evidence.
The veterinary supplement market is a pittance compared to the human market, but still a billion-dollar pittance that is growing rapidly. Unfortunately, the resources available for good quality research in veterinary healthcare are also a pittance, and it is not at all unusually for our pets to suffer, or even be euthanized, as a result of treatable diseases for want of money to pay for needed care. So $1 billion a year spent on nutritional supplements may not be such a good deal if these products don’t effectively prevent or treat disease.
The variety of supplements available is staggering. Many proprietary concoctions of vitamins, minerals, herbs, and other ingredients are marketed for health maintenance, “boosting the immune system,” retarding aging, or treating specific diseases. A comprehensive review of this multitude of moving targets is impossible. But the lion’s share of the pet supplement market goes to a few specific compounds, so I will focus on these. Most of these ingredients are also among the most popular supplements for humans, with a few exceptions, so there will be substantial overlap with previous discussions of the plausibility and evidence for many of these substances.
You can read specific, detailed evaluation of glucosamine, fish oil, probiotics, multivitamins, lysine, milk thistle, SAM-e, digestive enzymes, coenzyme-Q10 and Azodyl over there.
Don’t miss the balanced, useful “Bottom Line” section after the analysis of the individual supplements. There, SkeptVet answers the immediately salient question for many of us: should vets and pet owners use these products?