anxiety and stress
"I took this medicine for three months and stated to notice uncontrolled, constant muscle twitching in my feet and legs, that was 15 years ago.  Try to imagine your leg muscles twitching 24/7/365 for the rest of your life, that's what I'm dealing with and it's horrible.  I'd think twice before putting this chemical into your body.   Before this I was on Paxil for four years with pretty good results and no major side effects; wish I had stayed on that."