Chondroitin is a supplement, frequently used in conjunction with glucosamine, to combat the symptoms of osteoarthritis (OA).
A recent surge of meta-analyses (studies researching other studies) found that most studies that showed benefit with chondroitin were poorly designed or subject to chance statistical error (due to low amount of participants). Larger studies (which are seen as more reliable) tend to show no benefits with chondroitin nor glucosamine supplementation in isolation or combined.
Although many people do report benefit from using this supplement (especially when paired with Glucosamine), the current body of scientific literature does not hold these two supplements in high regard.