http://www.straightdope.com/columns/read/1276/do-copper-bracelets-ease-pain
One thing to mention is the concept of “regression to the mean;” generally, everything is cyclical and self-correcting, and usually people try alternative therapies when conventional therapies have failed and they’re subsequently at their worst; doing nothing would have had the same physical effect as trying something, because no matter what the pain would have diminished soon anyway.
Pain is notoriously hard to quantify and measure accurately, and is incredibly subject to the placebo effect, as well.