Chondroitin sulfate is a glycosaminoglycan chain of alternating Uronic acids and D-N-acetyl-galactosamine molecules bound by 1,3 bonds. They are produced in vivo to limited amounts and were initially extracted from animal sources, but are now industrially made via bacterial fermentation.
Supplementation of 1,200mg chondroitin sulfate, alongside glucosamine (hydrochloride), has failed to significantly increase circulating chondroitin concentrations either acutely or after three months of supplementation. This study did note that subjects had a baseline value of 20.8µg/mL chondroitin in one study arm and other studies which note lower baseline levels (0.3µg/mL) observed that 4,000mg chondroitin can increase circulating levels up to 5.3µg/mL after 2-6 hours.
Chondroitin appears to be eliminated primarily through the urine.
That being said, most recent meta-analyses indicate that the benefits gained from the combination or Chondroitin in isolation are not significantly different from placebo, and causation for improvement cannot be placed on the compounds themselves. It is mentioned that most studies finding benefit separate from placebo either have poor study design or inadequate sample sizes, whereas larger scale studies note no difference.
In effect, the scientific consensus of chondroitin at this time is one of uncertainty as it does not appear to be much different when compared to placebo.