Over consuming Vitamin B3 often leads to negative, but non-fatal health issues. Some of the common symptoms are Increased rate of heartbeat Redness and flushing of the skin Moderate to extreme faintness or vertigo Excessively itchy skin Stomach pains leading to vomiting Niacin overdoses happen largely because people think they can flush their systems with large amounts of the vitamin. Recommended Daily Allowance (RDA) for adults is between 16 and 18 mg daily, with a maximum intake of 35 mg daily

Hi Anything in excess is dangerous if not poisonous. So is with our vitamins. Excess B3 can give u anything from gastro disturbances to skin problems and an unnecessary  increase in heart rate. Any or all of the above may cause   disturbances in your well being. RDA is 18mgs per day (However it is based on the calorie intake) So avoid taking it in excess