Bupropion (aka - wellbutrin) is generally prescribed to treat depression, bipolar disease, and attention deficit disorder. It was recently approved by the FDA to assist in the cessation of smoking. Though one of its side-effects is drowsiness, this medication is not prescribed for insomnia.
Another side-effect, due to bupropion's upward effect on norepinephrine (noradrenaline), can be wakefulness.
The actual effect varies between individuals.