Vitamin B3 : Overdose...

People taking pharmacological doses of niacin (1.5 - 6 g per day) often experience a syndrome of side-effects that can include one or more of the following:

• dermatological complaints
• facial flushing and itching
• dry skin
• skin rashes including acanthosis nigricans
• gastrointestinal complaints
• dyspepsia (indigestion)
• liver toxicity
• fulminant hepatic failure
• hyperglycemia
• cardiac arrhythmias
• birth defects

Facial flushing is the most commonly reported side effect.It lasts for about 15-30 minutes, and is sometimes accompanied by a prickly or itching sensation. This effect can be blocked by taking 300 mg of aspirin half an hour before taking niacin, or by taking one tablet of ibuprofen per day. Taking the niacin with meals also helps reduce this side effect. After 1 to 2 weeks of a stable dose, most patients no longer flush.

Doses above 2 g per day have been associated with liver damage, particularly with slow-release formulations. High-dose niacin may also elevate blood sugar, thereby worsening diabetes mellitus.

Niacin for cholesterol

Niacin at doses used in lowering cholesterol has been associated with birth defects in laboratory animals and should not be taken by pregnant women.

Niacin at extremely high doses can have life-threatening acute toxic reactions. One patient suffered vomiting after taking eleven 500-milligram niacin tablets over 36 hours, and another was unresponsive for several minutes after taking five 500-milligram tablets over two days.

Extremely high doses of niacin can also cause niacin maculopathy, a thickening of the macula and retina which leads to blurred vision and blindness.