I was on 300 mg for about a year for depression and insomnia (two of the 150 mg trapezoid-looking tablets). It worked well for me (as far as the sleep aid part) when I remembered to take it and was not taking anything else, as this was during the time when I was still using. However, I started on 50 mg and ended up working my way up to 300 mg over a period of a couple of months.
I wish I was still on it! If I had insurance now, I would be!
The only negative side effect I had was a temporary groggy feeling for about 15 minutes when I first woke up and of course the wicked cotton mouth feeling in the morning. Had to keep a water bottle next to the bed for that reason.