I have written extensively about glucosamine because it is a ubiquitous arthritis therapy that nearly everyone seems to believe in and use, yet the evidence for it is poor. Only two published clinical studies are available for dogs, one showing no effect and one showing a marginal effect far less than that of non-steroidal anti-inflammatory medications (NSAIDs). Overall, the evidence is poor for the use of glucosamine in dogs, though it is limited in quantity. There appears to be little evidence of harm, however, there is no question NSAIDs are more effective by far, and overall quite safe, so it’s a shame that the caregiver placebo effect leads some vets and pet owners to deny dogs an effective treatment for their pain in favor of one that probably isn’t doing anything.
There is a great deal more evidence concerning glucosamine in humans, and though it is often conflicting, the general trend is that older, smaller, lower quality studies show a benefit and newer, better quality studies do not. Systematic reviews and meta-analyses generally conclude there is little chance this supplement is effective, and this was supported by the largest and best trial, GAIT. A study out of Australia has recently been published which appears to challenge the generally negative conclusions of the current literature, though the results are not unequivocal.
Fransen M, Agaliotis M, Nairn L, Votrubec M. et al. Glucosamine and chondroitin for knee osteoarthritis: a double-blind randomised placebo-controlled clinical trial evaluating single and combination regimens. Ann Rheum Dis. 2014 Jan 6. doi: 10.1136/annrheumdis-2013-203954. [Epub ahead of print]
This study followed slightly more than 600 people over two years, comparing glucosamine and chondroitin individually and in combination with placebo. The main outcomes of interest were changes in joint space narrowing and in self-reported pain. A number of secondary outcomes were evaluated also.
There were no effects of either supplement individually. The combination supplement did show a small change in joint space narrowing over the length of the study. If consistently seen, this change could be clinically significant and results in a small proportion of patients with knee arthritis (1 out of 14) avoiding a knee replacement surgery over a 2-5 year period of treatment. This might be more significant over a longer period, say 10-15 years. However, the statistical significance of this finding was borderline (p=0.046), so it is possible it was only a chance difference between the groups.
This interpretation is supported by the lack of similar effects found in other studies, and the lack of any significant difference in any other outcome evaluated in this study. The other primary outcome, pain, did not differ between the groups, suggesting no benefit of the supplement in terms of pain relief. While this study does show some potential benefit of glucosamine/chondroitin supplementation, in the context of the literature as a whole, it is not very impressive.
In terms of the veterinary use of these supplements, it is particularly concerning that this study and others consistently show no benefit over placebo in terms of pain. People frequently use glucosamine-containing supplements alone to treat arthritis pain in dogs and cats, and there is no convincing evidence they work. If we are being fooled into thinking they do, however, we are leaving our pets and patients to suffer with untreated pain. This is especially unfortunate given that safe and effective therapies for arthritis pain do exist. While there is likely no direct harm to using glucosamine, it is most likely a waste of money, and there is definitely a risk of indirect harm if it is substituted for weight loss, NSAIDs, and other arthritis therapies with better evidence of benefit.