FDA just announced that they are slapping a Black Box warning on Fluoroquinolone group of antibiotics. It appears that patients taking these drugs are increasingly likely to develop tendinitis or even tendon rupture.

"Tendon rupture can occur during or after completion of fluoroquinolone use; cases occurring up to several months after completion of therapy have been reported."

They have other undesirable side effects as well, it seems, like psychosis and suicidal tendencies.