can collagen peptides cause diarrhea？

Yes, it can happen, but it’s usually dose-dependent. Because true hydrolyzed collagen peptides have extremely high bioavailability, they are absorbed very rapidly in the small intestine. If a consumer takes a massive dose (like 30-40g) on an empty stomach, it can draw excess water into the digestive tract, causing an osmotic effect which leads to loose stools or diarrhea. Advising consumers to stick to a standard 10-15g daily dose usually solves this immediately.