Hi, Taking citalopram and Nucynta together is associated with the risk of developing serotonin syndrome which is a rare but serious disorder having symptoms like confusion, hallucination, seizure, extreme changes in blood pressure, increased heart rate, fever, excessive sweating, shivering or shaking, blurred vision, muscle spasm or stiffness, tremor, incoordination, stomach cramp, nausea, vomiting, and diarrhea. However since the dose of both citalopram and Nucynta is low in your case and since you do not have any options other than Nucynta, you can take the medicines as prescribed, while keeping a watch for any side effects. If however, your doctor prescribed Nucynta without knowing that you are on citalopram, then you should not start Nucynta without discussing this with him. Best wishes.