Well designed studies say no (see “Glucosamine and Chondroitin for Arthritis: Benefit is Unlikely” by Stephen Barrett, M.D. at Quackwatch. In brief: the largest and best study, the Gait or Glucosamine/Chondroitin Arthritis Intervention Trial, showed virtually no pain relief and an extension of the study showed no significant structural benefit, defined as slowing of the narrowing of the joint space in the knee). Another study specifically studied 250 adults with chronic low-back pain and degenerative arthritis for a year. Half received glucosamine and half placebo with no difference between the two. A more recent study involving 662 GAIT patients looked at glucosamine and chrondroitin sulfate, either separately or combined, and celecoxib (Celebrex) as well as a placebo. No statistically significant differences were found among the groups.
I myself took Glucosamine and Chondroitin for several months without positive effect, but then Celebrex at that time didn’t help either. There are people I know who claim they have been helped, especially by formulations with MSM, but it’s no miracle cure. So far there don’t seem to be any serious side effects of these supplements, but since supplements in general are not regulated, I’d be careful and also ask a doctor for advice. For a possible mechanism of action for glucosamine see “Food Intolerances: The Controversy Over Gluten Grains and Nightshade Plants: Do They worsen Arthritic and/or Intestinal Inflammation?