Niacin (vitamin B3) is available as a prescription medication and over‐the‐counter supplement. Although it is well known for its vasodilatory effect, it has also been associated with mild hepatotoxicity and, rarely, acute liver failure. We present the case of a 74‐year‐old Hispanic woman who developed acute liver failure (anicteric encephalopathy and coagulopathy) after her home dose of immediate‐release niacin was replaced with an extended‐release formulation during an inpatient hospital stay. This is the first reported case of niacin toxicity associated with a histopathologic finding of diffuse microvesicular steatosis. This unique phenotype strongly implicates mitochondrial impairment as a mechanism of niacin‐induced hepatotoxicity.
