A Case of Pellagra Induced by Isoniazid during Treatment of Pulmonary Tuberculosis Pellagra is a disease caused by a deficiency of nicotinic acid or niacin. It is mostly found among people eating corn-based diets in parts of China, Africa and India. It is also induced by drugs, such as isoniazid or 5-fluorouracil. Isoniazid inhibits the conversion of tryptophan to niacin and may induce pellagra, particularly in poorly nourished patients. Pellagra should be suspected whenever tuberculous patients under the treatment with isoniazid develop mental, neurological or gastrointestinal symptoms, even in the absence of typical skin changes.