restless legs syndrome
"Works great at getting rid of RLS, but causes rebound RLS after a few months of steady use.  Also doesn't affect RLS brought on or worsened by extreme tiredness or dehydration.  Rebound RLS is worse than before, and instead of having it a few times a week, RLS is constant after about 8pm, and rebound starts up in the very early AM.  It works well, but I started to have issues after several months."