OptiFlex-G is glucosamine sulfate, OptiFlex-C is chondroitin sulfate while OptiFlex Complete is one bottle each: OptiFlex-G (glucosamine sulfate) OptiFlex-C (chondroitin sulphate) Glucosamine and Chondroitin. Glucosamine is produced in the body and provides natural building blocks for growth, repair, and maintenance of cartilage. Chondroitin also occurs naturally and is part of a protein that gives cartilage elasticity. Glucosamine and chondroitin help cartilage absorb water and stay lubricated. Research suggests that when glucosamine and chondroitin are taken together, less glucosamine is absorbed. That is why OptiFlex Complete is formulated as separate doses of glucosamine (OptiFlex-G) and chondroitin (OptiFlex-C). Taking a full dose (2 tablets) of OptiFlex-G glucosamine in the morning and a full dose (2 capsules) of OptiFlex-C chondroitin in the evening should provide optimal results. With OptiFlex you have the option to take glucosamine or chondroitin alone.