Bupropion
"If I miss a dose I usually feel low energy return within 24 hours.  But feel fine once the right dose for me is reestablished.   I feel perfectly normal with 400 mg per day.  I don't feel well with less than that.  My wife needs 450 to control her SAD.  I feel sorry for people who give up before reaching an effective dosage of buproprion.  It takes a few weeks at the right dosage and after that you will feel like a new person."