However, other clinical trials have yielded mixed results. In 2011, the European Food Safety Authority Panel on Dietetic Products, Nutrition and Allergies concluded that "a cause and effect relationship has not been established between the consumption of collagen hydrolysate and maintenance of joints".[13] Four other studies reported benefit with no side effects; however, the studies were not extensive, and all recommended further controlled study.[14][15][16][17] One study found that oral collagen only improved symptoms in a minority of patients and reported nausea as a side effect.[18] Another study reported no improvement in disease activity in patients with rheumatoid arthritis.[19] Another study found that collagen treatment may actually cause an exacerbation of rheumatoid arthritis symptoms.[20] [21] [22]