There are three neurotransmitters in the brain called serotonin, norepinephrine and dopamine. SSRI's increase the levels of serotonin in the brain but not the other two.
Bupropion increases the levels of the other two neurotransmitters - norepinephrine and dopamine - in much the same way as SSRI's, by acting as an absorbent inhibitor.
Bupropion is often prescribed as an additional medication when SSRI's - which increase serotonin, are ineffective at treating depression.
Bupropion is also commonly used to treat nicotine-withdrawal effects for smokers who are trying to quit.
Unlike SSRI's, Bupropion does not normally cause weight gain or sexual dysfunction. However, side effects do include an increased risk of seizure.
Common brand names for Bupropion include Wellbutrin or Zyban.