Turmeric is pretty safe when taken under a doctors advise and supervision and most people never experience any negative side effects unless they take too much of the turmeric.
But the negative side effects that you may experience when taking turmeric are stomach upset, nausea, dizziness, or diarrhea and sometimes even a dangerous abnormal heart rhythm.
If you experience those side effects especially the abnormal heart rhythm then you should certainly speak to your doctor about it or go to urgent care or the emergency room for the abnormal heart rhythm side effect.