Vitamin B-3, which is also called niacin, is one of eight B vitamins that help the body convert carbohydrates into glucose for use as fuel. In addition, vitamin B3 is involved in the production of stress and sex hormones. Vitamin B-3 has been shown to reduce blood cholesterol levels and improve circulation, reports the University of Maryland Medical Center. Low doses of vitamin B-3 may cause mild side effects, although higher doses can cause more severe effects.
The most common side effect of vitamin B-3 is the so-called "niacin flush." People who take doses of 50 milligrams or more per day sometimes experience a tingling and burning sensation in the area of the chest, neck and face, which is accompanied by a red or flushed skin color. Skin may also become dry and itchy. Taking antihistamines or nonsteroidal antiinflammatory drugs before the vitamin B-3 may reduce the effects of niacin flush. This side effect often dissipates after one or two weeks of taking the vitamin, according to MedlinePlus.
Extremely high doses of vitamin B-3, greater than 1000 milligrams per day, can cause liver damage, reports the University of Michigan Health System. This damage to the liver can result in altered levels of liver enzymes in the blood; accumulation of fluid in the abdomen; a yellowing of the skin and eyes, known as jaundice; and potentially liver failure.
Gout and Ulcers
High doses of vitamin B-3 may also increase levels of a substance called uric acid in the blood. High levels of uric acid leads to the formation of uric acid crystals in the body, a condition known as gout, explains MedlinePlus. High doses of vitamin B-3 have also been known to cause stomach ulcers or worsen existing stomach ulcers.
Additional Side Effects
Mild side effects, such as stomachache and headache, may result from doses as low as 50 to 100 milligrams per day. Lightheadedness, dizziness and low blood pressure have also been reported after these lower doses of vitamin B-3. Heart palpitations and heart arrhythmia may occur in rare cases, according to MedlinePlus. Other rare side effects include anxiety, panic attacks, blood clotting problems and decreased thyroid function.