The Short Version
This claim oversimplifies a complex evidence landscape. While digestive benefits of collagen supplements do rest on thin, mixed evidence, joint and osteoarthritis outcomes are supported by multiple reviews and meta-analyses — making them comparably or even better established than cosmetic claims. Critically, recent high-quality analyses show that positive cosmetic results are largely driven by industry-funded, lower-quality studies, with independently funded trials finding no significant skin benefits. Grouping all non-cosmetic domains as uniformly "weaker" misrepresents the actual state of the science.