Hi, Welbutrin contains Bupropion used as an antidepressant. It acts by enhancing the action of Dopamine and Norepinephrine by increasing neuro-transmission and inhibiting re-uptake of Dopamine and Norepinephrine. Side effects are nausea, vomiting, dry mouth, dizziness, constipation, headache, etc. Cymbalta contains Duloxetine prescribed as an antidepressant. It acts by Serotonin and Norepihephrine reuptake inhibition. Side effects are nausea, dry mouth, constipation, headache, etc. Serotonin syndrome is the condition in which the serotonin levels in the brain get increased and disturbs the mood. Mild symptoms are diarrhoea and shivering. Severe symptoms are agitation, restlessness, increased heart rate and blood pressure, loss of muscle coordination, muscle rigidity, etc. Very severe symptoms are high fever, irritability, irregular heart beat and unconsciousness. If not treated on time, it may lead to death. Both Welbutrin and Cymbalta has side effect of serotonin syndrome. Regular check up helps to control the chances of serotonin syndrome. Symptoms should be observed for the possibilities of serotonin syndrome. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Pradeepraj, General & Family Physician