Dear patient, Methylphenidate may increase the blood levels and effects of FLuoxetine (prozac). You may be more likely to experience side effects, including a rare but serious condition like the serotonin syndrome you mentioned, which may include symptoms such as 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. Contact your doctor if you experience increased side effects or your condition changes during treatment with these medications. You may need a dose adjustment or more frequent monitoring by your doctor to safely use both medications. Since you have used the methylphenidat only temporarily, the chances of a serotonine are not high though. You may want to start the fluoxetine treatment after 3 days of not taking methylphenidate, and not mix those 2 medications in the future to be on the safe side. Hope this helps you, if you have any clarificatons you can get back to me, if this was helpful please kindly rate my answer. Best regards