Vitamin B3 (Niacin) Cautions

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Certain people should not take vitamin B3 (niacin) supplements at all:

People with a liver that is damaged or not working properly
People with an active peptic ulcer

People with the conditions listed above should not take vitamin B3 (niacin) supplements, especially at higher levels, as they could make their condition worse.

Certain people should not take vitamin B3 (niacin) supplements without first consulting their doctor for advice:

People with diabetes
People with gallbladder disease
People with glaucoma
People with gout
People with high blood pressure
People with liver disease

People with any of the conditions above may need to discuss vitamin B3 (niacin) supplementation with their doctor to ensure that they are getting the correct dosage that will not make their condition worse. People with the above conditions should not take high levels of vitamin B3 (niacin) as it may cause a worsening of their condition, which could be dangerous in some cases.

Certain people should not take vitamin B3 (niacin) supplements without first consulting their doctor for advice

Toxic Levels of Vitamin B3 (niacin)

Vitamin B3 (niacin) is has very limited (and reversible) toxicity and only at doses greater than 1-4g per kg of body weight per day. Niacinamide is toxic at levels higher than 2g (2000mg).

Overdosage and Toxicity Symptoms

Vitamin B3 (niacin) is a relative non-toxic vitamin, except at exceedingly high doses.

Acute levels (over 1-4g per kg of body weight) of vitamin B3 (niacin) can cause the following toxicity symptoms:

Abdominal pain
Abnormal liver function
Diarrhoea
Dry skin
Fainting
Fatty liver
Increased pulse and respiration
Instability in the genes of DNA (niacinamide toxicity)
Itchy skin
Jaundice (yellow skin and eye whites)
Liver damage (only at very high doses over a long time)
Low blood pressure
Nausea
Ulcer activation (only at very high doses over a long time)
Vomiting

People who experience any of the above toxicity symptoms should discontinue their vitamin B3 (niacin) supplements and seek the advice of their doctor. Toxicity symptoms are more likely to occur from taking too many supplements, whereas dietary intake of vitamin vitamin B3 (niacin) is highly unlikely to cause overdosage.

General symptoms of taking high (but not excessive) vitamin B3 (niacin) supplements include: