Hydroxyproline
Supplement
A component of gelatin and collagen, high doses of which theoretically raise concerns about kidney stones, though not observed as an adverse effect in studies.
Mentioned in 3 videos
Videos Mentioning Hydroxyproline

Breakfast, Glycine, Muscle Knots, and Trigger Points (Episode 48)
Stronger By Science
A component of gelatin and collagen, high doses of which theoretically raise concerns about kidney stones, though not observed as an adverse effect in studies.

Tools for Nutrition & Fitness | Dr. Layne Norton
Andrew Huberman
An amino acid derivative found in collagen, which helps stabilize its structure through hydrogen bonding. Its presence in collagen supplements might contribute to purported benefits for skin and connective tissue.

Doping, Collagen, Goals, and Hyperplasia (Episode 33)
Stronger By Science
An amino acid found in collagen and gelatin, high doses of which could potentially contribute to kidney stone formation.