332f662d_Supplements_for_Pain__effectiveness
[supplement & summary] Collagen. Extremely abundant proteinacious building block of connective tissue, currently popular as an arthritis treatment in the form of products like Genacol. Usually used for skin and nails. However, assuming extra collagen is helpful in any way, it is probably impossible to get it by eating it in the form of a supplement.17 [safety] probably safe — it’s just protein, and already a major component of other foods — but unstudied [more information] Scott Gavura’s collagen review for ScienceBasedMedicine.org [effectiveness] 
extremely limited and poor quality evidence
Supplements for Pain
effectiveness