Side Effects Of Excess Niacin

Niacin is also known as vitamin B3 or nicotinic acid. It is involved in regulating metabolism, DNA repair and steroid hormone synthesis. It is prescribed medically to treat high fat and cholesterol in the blood. Some people take the drug in the belief that it flushes out illicit drugs from the body or interferes with the results of drug screening, though this does not appear to be the case. Excess niacin can in fact be dangerous and cause side effects. If an overdose of niacin is suspected a person should seek emergency care.

Gastrointestinal Side Effects

Excessive amounts of niacin causes various side effects including problems with the gastrointestinal tract. These side effects may include abdominal pain, nausea and vomiting. It can also cause damage to the liver, and in severe cases cause the liver to fail. According to "Harrison's Principles of Internal Medicine" by Anthony Fauci, M.D, liver damage can be asymptomatic or manifest as right upper abdominal pain, yellowing of the skin, easy bleeding and bruising, swelling and a number of other possible symptoms.

Cardiac Side Effects

Excessive amounts of niacin can also cause cardiac arrhythmias. These are abnormal rhythms of the heart that can lead to inadequate delivery of blood to the body. Normally the top two chambers of the heart, the atria, contract to deliver blood to the larger bottom two chambers, the ventricles. The ventricles pump blood out to the lungs on the right and the rest of the body on the left. Rhythm disturbances can cause symptoms. Particularly severe arrhythmias can cause death. In less severe cases, they can cause chest pain, lightheadedness and weakness.

Skin Side Effects

A common side effect of niacin is skin flushing, even at therapeutic levels. Skin flushing is a reddening and increased temperature of the skin due to blood vessels dilating. It can also cause dry skin, itching and skin rashes, including a condition called acanthosis nigricans. This is a condition in which the skin becomes thickened and darkened, typically in body folds and creases such as the armpits. It is not unique to niacin toxicity, however.