70 patients with primary knee osteoarthritis were randomized to receive either 800 mg chondroitin sulphate (CS) or a placebo once a day for 6 months to determine the effects of CS on joint cartilage, assessed using magnetic resonance imaging (MRI). Results revealed that 800 mg chondroitin sulphate had an early effect (6 months) on cartilage volume loss and on bone marrow lesions at 12 months. Additionally, patients in the CS group who were taking non-steroidal anti-inflammatory drugs (NSAIDs) had significantly less synovial membrane thickness than patients in the placebo group taking NSAIDs. There were no significant differences in pain, function, stiffness, use of rescue medications or adverse events between the two groups.