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Vitamin B3
What is it? Overview Usage Side Effects and Warnings

Vitamin B3 Side Effects and Warnings

Written by ColleenO, FoundHealth.

Safety Issues

When taken at a dosage of more than 100 mg daily, niacin frequently causes annoying skin flushing, especially in the face, as well as stomach distress, itching, and headache.65 In studies, as many as 43% of individuals taking niacin quit because of unpleasant side effects.44

A more dangerous effect of niacin is liver inflammation. Although some reports suggest that it occurs most commonly with slow-release niacin, it can occur with any type of niacin when taken at a daily dose of more than 500 mg (usually 3 g or more). Regular blood tests to evaluate liver function are, therefore, mandatory when using high-dose niacin (or niacinamide or inositol hexaniacinate). This reaction almost always goes away when niacin is stopped. Note: Contrary to claims on some manufacturers' websites, there is no reliable evidence that inositol hexaniacinate is safer than ordinary niacin.

As noted above, a single dose of 2.5 to 5 grams of niacin (used in the vain hope of passing a urine drug test despite the presence of drugs in the system) can cause life-threatening disturbances in body function.70 Since this range includes the high-end of the dosage used for treating cholesterol, presumably people who gradually work up to taking several grams of niacin daily can accommodate it in a way that those who take it suddenly cannot.

If you have liver disease, ulcers (presently or in the past), gout, or drink too much alcohol,45 do not take high-dose niacin except on medical advice.

While there has been some concern that niacin may raise blood sugar levels in diabetics, the effect appears to be slight, and it carries little, if any, clinical significance.46,56,71

Combining high-dose niacin with statin drugs (the most effective medications for high cholesterol) further improves cholesterol profile by raising HDL (“good”) cholesterol.52-54 Unfortunately, there are real concerns that this combination therapy could cause a potentially fatal condition called rhabdomyolysis.

A growing body of evidence, however, suggests that the risk is relatively slight in individuals with healthy kidneys. Furthermore, even much lower doses of niacin than the usual dose given to improve cholesterol levels (100 mg versus 1,000 mg or more) may provide a similar benefit.55 At this dose, the risk of rhabdomyolysis should be decreased.

Nonetheless, it is not safe to try this combination except under close physician supervision. Rhabdomyolysis can be fatal.

Another potential drug interaction involves the anticonvulsant drugs carbamazepine and primidone. Niacinamide might increase blood levels of these drugs, possibly requiring reduction in drug dosage.50 Do not use this combination except under physician supervision.

The maximum safe dosage of niacin for pregnant or nursing women has been set at 35 mg daily (30 mg if 18 years old or younger).51

Interactions You Should Know About

If you are taking:

  • Cholesterol-lowering drugs in the statin family, niacin might offer potential benefits; however, there are real dangers to this combination. Do not try it except under physician supervision.
  • The antituberculosis drug isoniazid (INH): You may need extra niacin.
  • Anticonvulsant drugs such as carbamazepine or primidone: Do not take niacinamide except under physician supervision.

If you drink alcohol excessively:

  • Do not take niacin except under physician supervision.


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  2. Physicians' Desk Reference. Montvale, NJ: Medical Economics Co; 1999:1507.
  3. Elam MB, Hunninghake DB, Davis KB, et al. Effect of niacin on lipid and lipoprotein levels and glycemic control in patients With diabetes and peripheral arterial disease. The ADMIT Study: a randomized trial. JAMA. 2000;284:1263-1270.
  4. Bourgeois BFD, Dodson WE, Ferrendelli JA. Interactions between primidone, carbamazepine, and nicotinamide. Neurology. 1982;32:1122-1126.
  5. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B 6, Folate, Vitamin B 12, Pantothenic Acid, Biotin, and Choline (1998). The National Academies Press website. Available at Accessed October 4, 2001.
  6. Jacobson TA, Amorosa LF. Combination therapy with fluvastatin and niacin in hypercholesterolemia: a preliminary report on safety. Am J Cardiol. 1994;73:25D-29D.
  7. Kashyap ML, Evans R, Simmons PD, et al. New combination niacin/statin formulation shows pronounced effects on major lipoproteins and is well tolerated. J Am Coll Cardiol. 2000;35(suppl A):326.
  8. Wolfe ML, Vartanian SF, Ross JL, et al. Safety and effectiveness of Niaspan when added sequentially to a statin for treatment of dyslipidemia. Am J Cardiol. 2001;87:476-479.
  9. Wink J, Giacoppe G, King J. Effect of very-low-dose niacin on high-density lipoprotein in patients undergoing long-term statin therapy. Am Heart J. 2002;143:514-518.
  10. Grundy SM, Vega GL, McGovern ME, et al. Efficacy, safety, and tolerability of once-daily niacin for the treatment of dyslipidemia associated with type 2 diabetes: results of the assessment of diabetes control and evaluation of the efficacy of niaspan trial. Arch Intern Med. 2002;162:1568-1576.
  11. Mills EJ, Prousky J, Raskin G, et al. The safety of over-the-counter niacin. A randomized placebo-controlled trial [ISRCTN18054903]. BMC Clin Pharmacol. 2003 Nov 13. [Epub ahead of print]
  12. Mittal MK, Florin T, Perrone J, et al. Toxicity from the use of niacin to beat urine drug screening. Ann Emerg Med. Epub 2007 Apr 6.
  13. Goldberg RB, Jacobson TA. Effects of niacin on glucose control in patients with dyslipidemia. Mayo Clin Proc. 2008;83:470-478.


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