Overdosing on the ingredient nicotinamide hardly causes any side effects. However, if you take several grams of nicotinic acid, you may experience side effects such as nausea, vomiting or diarrhoea. In the worst case, long-term damage can even occur, such as problems with the liver. So-called "flush symptoms" can also occur. These are, for example, reddening of the skin and feelings of heat or hives.