Glucosamine (C6H13NO5) is an amino sugar and a prominent precursor in the biochemical synthesis of glycosylated proteins and lipids. Oral glucosamine is commonly used for the treatment of osteoarthritis. Since glucosamine is a precursor for glycosaminoglycans, and glycosaminoglycans are a major component of joint cartilage, supplemental glucosamine may help to rebuild cartilage and treat arthritis. Its use as a therapy for osteoarthritis appears safe, but there is conflicting evidence as to its effectiveness. A Cochrane 2005 meta-analysis of glucosamine for osteoarthritis found that only "Rotta" preparations (including older studies) found beneficial effects for pain and functional impairment. It also found that when only the studies using the highest-quality design were considered, there was no effect above placebo. Studies reporting beneficial effects have generally used glucosamine sulfate. Chondroitin is sometimes used in conjunction, and animal studies suggest that chondroitin may increase its efficacy. In 2008 a randomized, double-blind, placebo-controlled trial found glucosamine sulfate is no better than placebo in reducing the symptoms or progression of hip osteoarthritis.