Flexadin and UC-II. What 40 milligrams of collagen can do, and what the trials support

Flexadin Advanced is sold through vets and online and comes up regularly as a forum recommendation. Its main ingredient is called UC-II, and it works differently from everything else on the shelf: it is not dosed by weight.

What UC-II is

UC-II is a powder from chicken cartilage in which the type II collagen has not been altered by heat. The name is a trademark of the raw material's maker. On a label it usually appears as "UC-II chicken cartilage powder", on Flexadin at 40 mg per chew.

It is given as a small fixed amount per dog. Every trial gave dogs from about 15 to over 40 kg the same 40 mg a day. The trials themselves often write "10 mg active UC-II"; that is the same amount, counted against a different component. We store what the label states: 40 mg of the raw material.

Why "some evidence" and not more

There are several placebo-controlled trials in dogs with positive results, one of them measured on a force plate (Gupta and colleagues, 2012). That sounds good, and it is more than most joint ingredients can show. The limits are still considerable:

• The trials are very small, with five to ten dogs per group.
• They come mostly from one research group linked to the maker of the raw material.
• Their summaries do not say whether they were blinded.
• The only double-blind trial tested a mixture with frankincense and omega-3, so its effect cannot be put down to the collagen.
• The 2022 meta-analysis by Barbeau-Grégoire concludes that no effect of collagen can be established at present.

So we rate the amount but grade the evidence only as "some evidence". The 40 mg is the amount every trial gave, not the result of a dose-finding study.

Flexadin Advanced and Pro Agility side by side

Flexadin Advanced delivers 40 mg of UC-II in a 3 g chew, one chew a day at any weight, so it reaches the reference for every dog. It also contains frankincense extract, for which we have no reference, and vitamin E. Omega-3 is on the pack too, but what is declared is 84 mg of total omega-3, part of it from linseed oil, and 9.3 mg of EPA per chew. DHA is not stated, so we count the 9.3 mg. Against the joint target, that is a fraction of one percent.

Dr. Hölter Pro Agility is a powder with 0.8 % UC-II, plus 15.6 % green-lipped mussel, fish oil concentrate, glucosamine, chondroitin and MSM. The starting amount is 2.5 g per 10 kg. That gives 20 mg of UC-II per 10 kg, so the powder reaches 40 mg from about 20 kg of body weight; a 10 kg dog gets half. At the same amount the green-lipped mussel comes to about 39 mg per kilogram, in the middle of our reference range. For omega-3 only EPA is declared on its own, so here too we count the lower reading.

The two products do different jobs: Flexadin is a fixed amount of collagen for any weight, Pro Agility is a mixed powder that brings larger dogs into the reference range for UC-II and green-lipped mussel at once.

And cats?

For cats there is one randomised trial from 2026. The amount it used is only in the paywalled full text, and we could not read it. The dog amount cannot be carried over: it applies per animal rather than per kilogram, so there is no basis for scaling it down to a cat. For now we list no cat products with UC-II.

What comes before the collagen

For a dog moving differently than usual, the cause belongs established before anything is added to the bowl. What the other joint ingredients support is in the guide to joints in dogs. Supplements are not medicines.