Joints in cats. What data exists, and what follows from it
There are far fewer studies in cats than in dogs, and most products are derived from the dog. Which reference amounts we use, why they are less certain, and how to spot a product actually meant for cats.
Cats are under-represented in joint research. That is not an aside but the most important sentence here: most feline amounts are carried over from dogs rather than measured in cats. Anyone selling you the same confidence for cats as for dogs is selling a confidence that does not exist.
What we measure against, and what we no longer do
Two ingredients carry this category: green-lipped mussel and omega-3. Both have a reference amount with a source behind it, and both pages show where the figure comes from and how it is converted for your cat's weight. For the mussel the amount is carried over from dogs, because no feline trial exists. The page says so too.
Glucosamine and chondroitin no longer have a reference amount here. A 2022 meta-analysis went through 72 trials and found no benefit for that combination, with a result that in fact favours the control groups. Naming a target amount for an ingredient the best available review says does nothing would be a number without meaning. We still list products built on it, but we do not rate them.
The same goes for MSM: the span you see everywhere is a manufacturer convention, there is no dose-finding trial in dogs, and certainly none in cats.
Why products for cats are often under-dosed
Many joint products come in one size for dogs and cats. The feeding guidance then starts at "up to 10 kg: 1 scoop", and a 4 kg cat gets the same amount as a 9 kg dog. Per kilogram the cat is then at double. It happens the other way too: a chew sized for a 30 kg dog cannot sensibly be divided down for a cat.
A product genuinely meant for cats has its own weight bands below 10 kg, a form a cat will actually eat, and amounts per serving stated in milligrams.
With cats, acceptance is half the job
The best-dosed powder is worth nothing if it stays in the bowl. What helps in practice: start very small and build up over one to two weeks, mix the powder into wet food rather than sprinkling it on top, and give oil separately rather than stirring it into dry food, where it can go off.
What belongs with a vet first
If a cat jumps less, grooms differently, or changes its behaviour, the cause is a question for a vet and not for a supplement. Supplements are not a medicine. They can support everyday life, and no more than that.