Chondroitin sulfate is a substance that occurs naturally in the connective tissues of humans and animals, particularly in cartilage. It is commonly used as a dietary supplement, often in combination with glucosamine, to support joint health and manage symptoms of osteoarthritis. The scientific evidence for chondroitin sulfate's effectiveness is mixed but generally suggests a modest benefit, particularly in individuals with mild to moderate osteoarthritis.

Multiple randomized controlled trials and meta-analyses have evaluated chondroitin sulfate for osteoarthritis, especially of the knee. Some studies have found statistically significant, but generally small, reductions in pain and improvements in joint function compared to placebo. For example, a 2015 Cochrane review concluded that chondroitin may provide a small to moderate improvement in pain and function. However, other large, well-designed trials, such as the GAIT study, reported limited or no benefit over placebo. Safety profiles are generally favorable, with few serious adverse effects reported.

Overall, scientific consensus is that while chondroitin sulfate is not a cure and may not work for everyone, it may offer symptomatic relief for some people with osteoarthritis, particularly when used for at least several months. Its use is primarily justified by scientific studies, though the quality and outcomes of these studies vary, resulting in a moderate evidence rating.