What are type II collagen’s main drawbacks?

By and large, CII seems fairly safe. One potential concern is that collagen (in dosages of around 10 grams per day) has been shown to increase oxalate levels in urine, likely because collagen consists of approximately 10% hydroxyproline, and a major metabolite of hydroxyproline is oxalate. As a result, higher doses of CII could increase the risk of oxalate-based kidney stones in susceptible individuals.