Hydroxyproline is an amino acid derivative your body makes from proline after collagen fibers are assembled. It acts as a structural anchor that keeps collagen stable and resilient. You do not need to take it as a supplement because your cells produce all they require when you consume proline and enough vitamin C.
Oral hydroxyproline does not get channeled directly into new collagen. Any dose that survives digestion is largely ignored by collagen-building pathways. The body prefers to make its own supply on site.
You will rarely see isolated hydroxyproline sold as a standalone product. Unlike collagen peptides or gelatin, no clear functional use exists for it in dietary supplements, and no recognized daily intake has been set.