A Norwegian study published in the AMA Journal supported the pharmaceutical industry by claiming that glucosamine does not work for arthritis in the low back. They were able to do so by using only half the effective dose of 3 Gm per day and omitting cofactors, especially MSM and certain herbals like boswellia. I find that the liquid glucosamine/MSM combo preparation works better than the pills for most patients. Glucosamine does not work for everyone, but neither does Motrin, Celebrex, or Alieve, which cause way more side effects in the stomach, kidneys, and heart.
See JAMA 2010;304(1):45-52.