The most common side effect seen with various niacin products is flushing of the face and trunk. This side effect, known as the niacin flush, is harmless but often severe enough that many people stop taking the vitamin. In order to help prevent the flush, you should always start with a low niacin dosage and gradually work your way up to a higher dose.
Niacin (brand names include Niacor®, Niaspan®, Slo-Niacin®, and several others) is a vitamin available both as non-prescription nutritional supplements and as prescription medications. It is most often used to improve cholesterol levels, as it can have beneficial effects on HDL cholesterol, LDL cholesterol, and triglycerides. Although niacin remains the most effective medication for increasing HDL cholesterol ("good cholesterol"), its usefulness is limited by a bothersome and sometimes intolerable side effect, known as the niacin flush.
Niacin very predictably causes flushing. Flushing is a warm, tingling, itching feeling of the skin accompanied by redness of the skin. It occurs most commonly in the face and the trunk, although it can occur from head to toe. Flush can be extremely uncomfortable and may be accompanied by a rapid heartbeat, chills, shortness of breath, sweating, dizziness, and even fainting.
Niacin causes flushing by dilating (expanding) the blood vessels on the surface of the skin. Although this side effect of niacin is harmless, it is often severe enough for people to stop taking niacin.