Niacin - side effects and warnings

Side Effects and Warnings
Most people taking niacin experience skin flushing and a warm sensation, especially of the face, neck and ears, when they begin treatment or increase dose. This reaction is usually mild, but has been intolerable enough to cause up to half of participants in studies to stop therapy. Dry skin and itching is also commonly experienced. Taking aspirin or non-steroidal anti-inflammatory drugs such as ibuprofen (Advil®, Motrin®), naproxen (Naprosyn®), or indomethacin (Indocin®) can reduce the flushing. Use of an antihistamine 15 minutes prior to a niacin dose may also be helpful. Slow-release niacin products may have less skin flushing than regular release niacin preparations or may simply delay the appearance of flushing. The flushing response often decreases on its own after 1 to 2 weeks of therapy. Mild stomach upset, nausea, vomiting and diarrhea also may occur when beginning niacin therapy, and usually resolve with continued use.

More serious side effects include liver toxicity, worsening of stomach ulcers, and altered blood chemistry levels (increased blood sugar and uric acid concentrations). Numerous case reports describe liver toxicity, including increased liver enzyme levels in the blood, skin yellowing (jaundice), fluid in the abdomen (ascites), or liver failure. Monitoring of liver blood tests while using niacin is recommended. While slow-release niacin products may have less skin flushing than regular release niacin preparations, they may worsen stomach and liver side effects.

Niacin can cause significant alterations in blood sugar levels and insulin. This has been a potential concern in patients with diabetes, although a recent randomized controlled trial reports that of 148 patients, only 4 discontinued niacin because of inadequate glucose control (doses of 1000-1500 mg per day in a controlled release formulation were used). Nonetheless, caution is advised in patients with diabetes or hypoglycemia, and in those taking insulin, drugs, herbs, or supplements that affect blood sugar. Serum glucose levels may need to be monitored by a healthcare provider, and medication adjustments may be necessary. Although niacinamide is generally not associated with other side effects, it may affect insulin and blood sugar levels.

In theory, gout may occur during niacin treatment, due to increased blood uric acid levels. Lactic acidosis has been reported after taking sustained-release niacin. Niacin-induced muscle cell damage (myopathy) and increased blood levels of creatine kinase (a marker of muscle damage) have been reported in studies.

Abnormal heart rhythms and heart palpitations have occurred in niacin studies. Based on human research, taking niacin alone or with colestipol may increase blood homocysteine levels. High levels of homocysteine have been associated with an increased risk of heart disease.

Blood clotting problems have been reported during treatment with sustained-release niacin. Caution is advised in patients with bleeding disorders or taking drugs that may increase the risk of bleeding. Dosing adjustments may be necessary. Low white blood cell number (leukopenia) and slightly increased blood eosinophils have also been reported.

Rarely reported side effects include headache, tooth or gum pain, dizziness, breathing difficulty, increased anxiety, panic attacks, and decreased thyroid function (hypothyroidism). There are published accounts of temporary side effects of the eye including macular swelling and blurred vision as well as toxic amblyopia ("lazy eye"). These side effects resolved when niacin was stopped.