In a new study, researchers analyze data from 15 studies of these compounds.
"We found that the drugs do work on symptoms -- mobility, pain relief, quality of life -- and that they are very safe," lead researcher Florent Richy, MSc, an epidemiologist with the University of Liege, Belgium, tells WebMD.
In fact, glucosamine seems to slow the progression of osteoarthritis, which no other drug claims, says Richy. Osteoarthritis, also known as degenerative joint disease, is the most common form of arthritis and leads to loss of joint cartilage, the cushioning between bones.
But Kent Kwoh, MD, professor of rheumatology at the University Pittsburgh School of Medicine, is skeptical. The studies of glucosamine and chondroitin have involved too few patients, and been too flawed, to be taken as definitive, he says.
"There's been a lot of controversy about this medication," Kwoh tells WebMD. "Some X-rays of joints don't provide a really good picture of the joint narrowing, so it's difficult to tell whether arthritis has worsened or not."
Glucosamine sulfate and chondroitin sulfate are components of natural joint cartilage. They are thought to help slow the loss of cartilage -- called joint space narrowing -- seen with osteoarthritis by stimulating production of new cartilage. In addition, the supplements are reported to provide pain relief and greater joint flexibility.
The supplements are widely sold in health food stores and through the Internet. While studies have found at least some perceived benefit among users, the results have been somewhat controversial.
The studies in Richy's analysis all focused on osteoarthritis of the knee. Richy and his colleagues carefully selected only the most reliable studies -- "the best available evidence," he tells WebMD. Though they found fewer good studies of chondroitin, they found ample evidence for glucosamine alone and the two compounds together.
The analysis focused on 15 studies of 1,775 patients -- 1,020 taking glucosamine and 755 taking chondroitin -- which showed "significant changes" in the symptoms of patients taking them, Richy writes. No placebo group showed this kind of improvement, he adds.
Among the findings:
- Glucosamine significantly improved joint space narrowing. Though two chondroitin studies showed comparable results, there were not high-quality, detailed articles to support the findings, says Richy.
- Both supplements significantly reduced symptoms such as pain, stiffness, physical functioning, and joint mobility from the two compounds.
- Symptom improvement began about two weeks after starting the supplements.
- Glucosamine can slow down the progression of osteoarthritis. "It doesn't have a huge effect, and for the worst cases cannot make miracles, but it does slow down the process," Richy tells WebMD. Glucosamine did not restore cartilage, he says.
- Taking at least 1,500 mg of oral glucosamine sulfate for at least three years was most effective in slowing the degenerative process.
- While there were similar findings on chondroitin, those findings were not as clear-cut.
Overall safety of glucosamine and chondroitin "can be considered excellent," writes Richy. There are substantial beneficial effects on symptoms of glucosamine and chondroitin therapy compared with placebo, he adds.
One caveat: It's important to point out that anti-inflammatory pain relievers such as ibuprofen and naproxen were allowed in all studies, he says. Still, taking the supplements and anti-inflammatory drugs at lower doses was more effective at reducing pain than placebo or anti-inflammatory drugs alone, Richy says.