Brand explained the disagreement better than anything else did
Brand cut the disagreement between 25 glucosamine trials by 41%: one maker's twelve trials showed a large benefit, the other thirteen none. In that maker's three best trials it was small.
What the study found
The brand effect mostly dissolves in that brand's own best trials
Brand explained more of the disagreement between 25 glucosamine trials than anything else, cutting it by 41%: one manufacturer's twelve trials showed a large benefit and the other thirteen showed none. Inside that manufacturer's three least-biased trials, it shrank to a small one.
The caveat · Brand and trial quality are tangled
Risk of bias was the second-largest explanation, cutting the disagreement by a further 32%, so brand and how well a trial was run stay entangled. The shrunken estimate rests on three trials, and even after both factors the trials still disagree substantially. Pain only, nothing on joint structure.