The vitamin has been observed and studied to be safe for almost everybody when it is taken by the mouth. However, it has been recently established that Niacinamide causes flushing which can cause some disadvantages in terms of severity. If Niacinamide is taken without adhering to the protocols of safety and precautions then it can cause some minor effects such as intestinal gas, redness of the skin, itchiness, or nausea.