Taking glucosamine for six months did no more to ease chronic lower back pain than taking a dummy pill, Norwegian researchers said.

They said the widely used treatment appears to offer little benefit to patients whose aching back is caused by degenerative arthritis, and they said doctors should not recommend it for their patients. Studies of glucosamine, a dietary supplement, have been mixed, with some small studies showing a benefit in certain patients, such as those with osteoarthritis of the knee.

A team led by Philip Wilkens of Oslo University Hospital and University of Oslo did a randomised clinical trial -- the most scientifically rigorous kind -- to see what effect glucosamine had in 250 people over 25 with chronic lower back pain. They assessed people in the study at six months and again at one year using a pain and disability questionnaire and found no statistically significant difference in scores between the group that took the supplement and the group that took a dummy pill.

"Based on our results, it seems unwise to recommend glucosamine to all patients with chronic lumbar pain and degenerative lumbar osteoarthritis," Wilkens and colleagues wrote in the Journal of the American Medical Association . Dr. Andrew Avins of Northern California Kaiser-Permanente in Oakland, California, said in a commentary that given the high quality of the study, the most likely explanation of the findings is that "glucosamine probably offers little benefit for chronic low back pain with osteoarthritis beyond whatever placebo effect it may provide."

Dr. John Markman, a pain specialist at the University of Rochester Medical Center in New York, called the study a setback because glucosamine "is inexpensive and has few side effects, compared to other treatments." He said 80 percent of the U.S. population will have back pain in their lifetimes, with U.S. spending about $16 billion a year to treat it.