There have been no clinical trials on fibromyalgia, but there is a lot of anecdotal evidence that it works very well. 200 mg 3x a week. There are some potential side effects, but they have been described by the American College of Rheumatology as infrequent and mild. It is considered one of the safest antibiotics. Another key reason for its benign profile is that it is in a class of antibiotics least likely to encourager resistant strains.
Some people take it for decades.
Others for just a few months. Some people take them indefinitely. It's a case of early treatment equals in many cases early remission. Later treatment takes longer because the bug is more entrenched. This is primarily for RA, but there have been recents indications that it works to a lesser degree, probably less as an antibiotic than as a disease modifier, for osteo.