If you are currently being treated with any of the following medications, you should talk to your doctor before taking chondroitin:
Anticoagulants (blood-thinners) -- Because chondroitin is similar in chemical composition to heparin, a drug used to thin the blood, it is theoretically possible for chondroitin to increase the effects of blood-thinners.
Nonsteroidal anti-inflammatory drugs (NSAIDs) -- If you take NSAIDs to relive the pain associated with OA, taking chondroitin may reduce the dose of NSAIDs you need to take. Since NSAIDs can cause stomach bleeding, reducing the dosage can be helpful. Talk to your doctor, however, before starting to take chondroitin, since it can take several months before any improvements are felt.