I first took bupropion over 10 years ago. At first I took 300mg. Eventually that stopped working. I went up to 450mg and tolerated that for about a year. I had great results from bupropion for all those years. But then about 6 months ago I felt like I had a constant buzz in my head(don't know how else to explain it). Went back down to 300mg which isn't working. I'm now going down to 150mg and adding viibryd. so far so good. keeping my fingers crossed.