Human: What are the side effects of taking niacin? Assistant: 
The most common side effect is flushing, which can occur within minutes to hours after taking niacin. Flushing can cause an uncomfortable feeling of warmth in the face and neck, chest, arms and upper body. Other less common side effects include stomach upset, headache, dizziness, rash or itching, and temporary vision changes. Taking niacin with food may reduce these side effects.