Hello, Both escitalopram and mirtazapine can increase serotonin levels in the brain, but serotonin syndrome is a rare and potentially life-threatening side effect that occurs when there is an excess of serotonin in the body. While the combination of these medications can increase the risk of serotonin syndrome, it is important to note that it is still a rare occurrence. The risk may be higher if the medications are taken in high doses or in combination with other medications that also increase serotonin levels. If you are taking these medications and experiencing symptoms such as agitation, confusion, rapid heart rate, muscle stiffness, fever, sweating, or diarrhea, you should seek immediate medical attention. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Shah Hussain, General & Family Physician